What's the LinqToXML xaml equivalent of .Distinct()?

What's the LinqToXML xaml equivalent of .Distinct()?

Here's the DisplayMemberPath property binding for my ListBox (I'm binding
to an ObservableCollection of XElements):
DisplayMemberPath="Element[Shape].Value"
I've used linq many times for parsing Entity Framework and Sql data, in
which case I would write the analogous binding:
DisplayMemberPath="PropertyName.Distinct()"
I don't want to filter my actual collection to only return Distinct
values--I want my full collection and only display distinct values to
mitigate collection building and PropertyChanged notifications.
Alternative thought: Could I use my ObservablecCollection "getter" to grab
the distinct values of the full list set in the setter? (Not sure if that
makes sense...) so the true collection remains non-distinct and the
displayed collection becomes distinct?