Bind to parent control from within context menu within data template - wpf

Question

I'm wanting to bind to a parent control from a context menu within a datatemplate.
Unfortunately I'm restricted to .net 3.5 and can't use the x:reference extension introduced in .net 4.
Below is an example of what I'm trying to do
<Window x:Class="WpfApplication17.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication17"
Name="window">
<Window.Resources>
<DataTemplate DataType="{x:Type local:Car}">
<Rectangle Width="100" Height="100" Fill="Red">
<Rectangle.ContextMenu>
<ContextMenu>
<MenuItem Header="{Binding Colour}"/>
<MenuItem Header="{Binding ElementName=window, Path=ActualWidth}"/>
</ContextMenu>
</Rectangle.ContextMenu>
</Rectangle>
</DataTemplate>
</Window.Resources>
</Window>
But I get "Cannot find source for binding with reference 'ElementName=window'" error due to the context menu not being part of the visual tree.
Edit :
That works great! .. however, it doesn't seem to work when I use a composite collection such as the following
<Window.Resources>
<DataTemplate DataType="{x:Type local:Car}">
<Rectangle Width="100" Height="100" Fill="Red"
Tag="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}}">
<Rectangle.ContextMenu>
<ContextMenu>
<ContextMenu.ItemsSource>
<CompositeCollection>
<MenuItem Header="{Binding Colour}"/>
<MenuItem Header="{Binding Path=PlacementTarget.Tag.ActualWidth, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
</CompositeCollection>
</ContextMenu.ItemsSource>
</ContextMenu>
<!--<ContextMenu>
<MenuItem Header="{Binding Colour}"/>
<MenuItem Header="{Binding Path=PlacementTarget.Tag.ActualWidth, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
</ContextMenu>-->
</Rectangle.ContextMenu>
</Rectangle>
</DataTemplate>
</Window.Resources>

Answer 1

Please try this:
<DataTemplate DataType="{x:Type local:Car}">
<Rectangle Width="100" Height="100" Fill="Red"
Tag="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}}">
<Rectangle.ContextMenu>
<ContextMenu>
<MenuItem Header="{Binding Colour}"/>
<MenuItem Header="{Binding Path=PlacementTarget.Tag.ActualWidth, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
</ContextMenu>
</Rectangle.ContextMenu>
</Rectangle>
</DataTemplate>
See my answer here too.