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.