I wonder if you still have access to the mashine if your GPU freezes?! If you are running Linux and still have access via SSH for example you could try rmmod/modprobe the driver. Or reenable the CTRL+ALT+BACKSPACE combination /etc/inittab in order to kick and restart the X Server (might still be enabled in your distro) if your keyboard is still alive and being polled by the kernel. Furthermore you might be able to drop to a debug shell if you have Magic System Request enabled in your kernel. But i doubt you might be able to recover from there.
This all are no out-of-the-box solutions and chances are not too high you succeed with any of them, but you might want to tinker with this options if you are using Linux.
Hrmmm, nice idea!
You're right, just because my desktop is frozen doesn't mean that SSH shouldn't work...
I will give 'er a try, thanks!