It would be cool if the correct answer was provided...
This is what I did:
Simply define the context menu to have no items...
Then define the context menu template like this:
This produces a pane with no buttons or menus...which is what the posters I believe were asking...setting the template to x:Null does not hide the menu button which I think was the objective...
I'm using 2010 Q1 controls.
HTH, Steve