DavyGT, then You can use 100k ohm VR.
It depends to what these resistors are connected. I never use pencil-mods and don't recommend it.
For Vgpu You can use PWM cap legs for example. Similar to: http://ceemic.pri.ee/hardware/hd4850..._mod01_mon.jpg
Do a layout pic so we can suggest the best place for measuring.