WPF Databinding: How do I access the "parent" data context?

This will also work:

<Hyperlink Command="{Binding RelativeSource={RelativeSource AncestorType=ItemsControl},
                             Path=DataContext.AllowItemCommand}" />

ListView will inherit its DataContext from Window, so it's available at this point, too.
And since ListView, just like similar controls (e. g. Gridview, ListBox, etc.), is a subclass of ItemsControl, the Binding for such controls will work perfectly.

You could try something like this:

...Binding="{Binding RelativeSource={RelativeSource FindAncestor, 
AncestorType={x:Type Window}}, Path=DataContext.AllowItemCommand}" ...