How to Disable default context menu on mouse right click in Silverlight4

Question

Hi,
I want to disable default context menu ("Silverlight" text comes on mouse right click)
on mouse right click.
I tried the following, 
1. Register mouse right click event
2. In Event I have write e.handler = true;

Observation:
The above event is fires everytime when I right click
But not fires when I write any text in AutocompleteBox and hence the default context menu coming.
I tried to register the same event on AutocompleteBox_MouseRightClickDown() but it was not firing when autocompletebox get focussed (Display matched items in textbox window)

Please help me out to resolve this?

Thanks!