For the Vgpu mod, try connecting a 100k VR between one of the yellow points and ground. I'm not sure about the exact VR value, but 100k should be reasonably safe.
There's a possibility that there will be no voltage increase visible with a 100k VR. If this is the case, power off and decrease the resistance by a quater. Repeat this until the voltage starts to increase. If the voltage doesn't increase after reaching about 5k, I'll have another look at the mod.

note: XS owners and members will not be liable for any damage caused to you or your hardware, neither can be liable for any breach of the warranty.