Detecting a "grabEnter"?

[dfepstein at comcast.net]

My question about "grabEnter" has led to an interesting broader discussion of the relative merits of grab vs mouseMove..
I would be happy to write a more complicated "mouseMove"-controlled script, but as far as I can tell that won't solve the problem I posed. If the user is dragging an object, whether using "grab" or by a script reacting to "mouseMove" events, no objects beneath that object receive a mouseEnter or mouseLeave message, because the mouse remains within the object being dragged.
I can think of ways of amending Transcript that would solve this problem--probably by extending the current usage of the various messages associated with drag and drop actions. But is there any way to do what I want with the language as it is? Capturing "mouseMove" doesn't tell me "what control the dragged object has just moved on top of" unless at each nudge of the mouse I compare the mouseLoc with the rectangles of all potential target objects.
David Epstein