New Post: WinRT navigation service

I'm trying to implement a Hierarchical navigation and a Flat one in the same app.

http://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh761500.aspx

Basically this: The top Bar has menu items (1 or more) and when selected it starts a hierarchical navigation.  

So is it possible to replace the INavigationService that is passed around each ViewModel?

I'm guessing I would need to create a new FrameAdapter with a new Frame, but then how do I tell the WinRTContainer to use that new one INSTEAD of the one created at startup?

Of any other ideas ?