Classic Drawing problem

Here's the jist of it: (classic drawing problem)

I need to be able to draw some stuff on a graphics object. When the user selects a shape, the outline of the shape moves with the mouse cursor until they click on the drawing surface, where it becomes planted onto the surface. In the meantime, I don't want the outline shape to erase over what's underneath while the user is moving the mouse cursor.

Seems to me that to solve this I need to have two region objects... and invalidate the underlying region as the outline moves across it....