[PyMOL] ray-trace stop button?

Is there any way of stopping a ray trace once it has been started without
closing pymol?  Some of my ray trace jobs take too long and I want to stop
them.  I've also noticed that pymol doesn't close very elegently during a
ray trace job.  I'm working on a windows pc and the "end task" approach
sometimes doesn't seem to work at all, forcing me to reboot.  

-Mark