I did some searching and it seems that there is indeed a way to bind/unbind the GPU from the host by writing to /proc/bus/cpu, but apparently this is (was?) not always very stable as some GPU firmwares (AMD in particular it seems) do (did?) not allow resetting the device through any firmware interfaces.

If anyone knows if this is still the case and if the same holds for modern NVidia cards as well that would be great! Is GPU reset a documented/officially supported feature on NVidia/AMD these days?