Hi John,
You can query the mouse / modifier keys using MEvent, but as far as I know it only works from MPxContext derived classes, and sadly my callback has nothing to do with contexts.maybe there is a way to ignore the callback if a mouse button is pressed down at the time. (or the alt key, if this is the main issue).
Please correct me if I'm wrong, actually I'd be really happy to be wrong!
Cheers, Szabolcs -- http://groups.google.com/group/python_inside_maya
