Still no takers on this problem?

I believe you could use the Header property to set a custom content, in this snippet I use a Rectangle element:

<Intersoft:UXStackItem Text="Automator" FontSize="12" Margin="0" Height="64" VerticalAlignment="Top">
	<Intersoft:UXStackItem.Header>
		<Rectangle Fill="Blue" Height="100" Stroke="Black" Width="100"/>
	</Intersoft:UXStackItem.Header>
</Intersoft:UXStackItem>

Okay, here is what I've been trying to do and I think I may have uncovered a bug in the UXDesktopDockButton control:

I have a datasource with a propery of type UIElement that I'm trying to bind to the Icon property of the UXDesktopDockButton.  I created a converter that will convert the UIElement to a WriteableBitmap at the time of binding.  Now I can get the converter to work just fine on an Image control's Source property, but on the UXDesktopDockButton's Icon property I get a blank button.  See the sample code below or the attached project to recreate the issue:

Note: Ignore the bit about the DataTemplate in the converter, that code is not used yet. 

Coverter Code:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Media.Imaging;
 
namespace SilverlightPlayground
{
    public class DependencyObjectToImageSourceConverter : IValueConverter
    {
 
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            int height = 16;
            int width = 16;
 
            if (parameter != null)
            {
                if (parameter is string)
                {
                    string rawParameter = parameter as string;
                    string[] paramArray = rawParameter.Split(',');
                    if (paramArray != null && paramArray.Length > 0)
                    {
                        int.TryParse(paramArray[0], out width);
                        int.TryParse(paramArray[1], out height);
                    }
                }
            }
 
            if (value is UIElement)
            {
                UIElement element = (UIElement)value;
                if (element is FrameworkElement)
                {
                    ((FrameworkElement)element).Width = width;
                    ((FrameworkElement)element).Height = height;
                }
                WriteableBitmap bitmap = new WriteableBitmap(width, height);
                bitmap.Render(element, null);
                bitmap.Invalidate();
 
                return bitmap;
            }
            else if (value is DataTemplate)
            {
                UIElement element = ((DataTemplate)value).LoadContent() as UIElement;
                if (element is FrameworkElement)
                {
                    ((FrameworkElement)element).Width = width;
                    ((FrameworkElement)element).Height = height;
                }
                StackPanel grid = new StackPanel();
                grid.Background = new SolidColorBrush(Colors.Green);
                grid.Width = grid.Height = 300;
                grid.Children.Add(element);
                ((Grid)((UserControl)Application.Current.RootVisual).Content).Children.Add(grid);
                grid.UpdateLayout();
                WriteableBitmap bitmap = new WriteableBitmap(width, height);
                bitmap.Render(grid, null);
                bitmap.Invalidate();
                //grid.Children.Remove(element);
                Image img = new Image();
                img.Source = bitmap;
                grid.Children.Add(img);
                grid.UpdateLayout();
                return bitmap;
            }
            return value;
        }
 
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

MainPage.xaml:

<UserControl xmlns:Intersoft="http://intersoft.clientui.com/schemas"  x:Class="SilverlightPlayground.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:converters="clr-namespace:SilverlightPlayground"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    <UserControl.Resources>
        <converters:DependencyObjectToImageSourceConverter x:Key="DependencyObjectToImageSourceConverter"/>
    </UserControl.Resources>
    <Grid x:Name="LayoutRoot" Background="White">
        <Image x:Name="BoundImage" Source="{Binding SomeUIElementProperty, Converter={StaticResource DependencyObjectToImageSourceConverter}, ConverterParameter='200,50'}"/>
        <Intersoft:UXDesktopDock>
            <Intersoft:UXDesktopDockButton Text="Test Button" Icon="{Binding SomeUIElementProperty, Converter={StaticResource DependencyObjectToImageSourceConverter}, ConverterParameter='50,50'}" />
        </Intersoft:UXDesktopDock>
    </Grid>
</UserControl>

MainPage.xaml.cs:

using System.Windows;
using System.Windows.Controls;
 
namespace SilverlightPlayground
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
            this.DataContext = this;
        }
 
        public UIElement SomeUIElementProperty
        {
            get
            {
                Grid grid = new Grid();
                TextBlock text = new TextBlock();
                text.FontSize = 12;
                text.Text = "Hello World!";
                grid.Children.Add(text);
                return grid;
            }
        }
    }
}

I'm not talking about the UXStackItem, I'm talking about using the UXDesktopDockButton or just the UXDockButton.  They don't have a Header property. 

When using the UXStackItem, I can just specify an IconTemple instead of an Icon.  This is not possible in the UXDockButton. 

Actually, UXDesktopDockButton has a content property and which you could use to hold the IconTemplate. Here is a simple snippet of UXDesktopDockButton containing a TextBlock element:

<Intersoft:UXDesktopDockButton>
    <TextBlock Text="Hello World!"/>
</Intersoft:UXDesktopDockButton>

In the attached sample, such scenario will be incompatible with the default ImageLoader in the UXDesktopDockButton so you will need to disable the ImageLoader in the DesktopDock.

<Intersoft:UXDesktopDock UseImageLoader="False">

Turning off the image loader did the trick!  Thanks!

I couldn't get the Content property to work, though.