Drawing outside of a given region

Here is the problem---->

We are trying to create a selection rectangle, similar to
the rectangle that is drawn when you try to hold the mouse button down and
drag it in the Photon Application Builder. However, in the PhAB, you can
drag in and out of regions and the PhAB seems to be able to determine how to
draw the rectangle anyway.

The way we have it set up is the events are added to the
PtRaw widget and if the user starts dragging inside and ends up outside of
the region we have know way to determine what the coordinates are OUTSIDE of
the region. Any help would be appreciated.