TemplateBinding in ItemsPanelTemplate

Question

I'm building a custom ItemsControl in Silverlight that (amongst other things) allows items to be displayed horizontally or vertically at runtime. How can I bind the Orientation property of the ItemsPanel to the Orientation property of my parent control? I've tried using TemplateBinding (which works inside the ControlTemplate) but does not seem to work inside the ItemsPanelTemplate, am I doing something wrong?

<Style TargetType="CustomItemsControl">
    <Setter Property="ItemsPanel">
        <Setter.Value>
            <ItemsPanelTemplate>
                <StackPanel Orientation="{TemplateBinding Orientation}" />
            </ItemsPanelTemplate>
        </Setter.Value>
    </Setter>
</Style>

Answer 1

Use a RelativeSource:

<Style TargetType="CustomItemsControl">
    <Setter Property="ItemsPanel">
        <Setter.Value>
            <ItemsPanelTemplate>
                <StackPanel Orientation="{Binding Orientation, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type CustomItemsControl}}}" />
            </ItemsPanelTemplate>
        </Setter.Value>
    </Setter>
</Style>

Edit after comment: Silverlight doesn't support RelativeSource, but this post by Colin Eberhardt explains how it can be implemented manually.