Dito to all that ceemic said so far.

@Ket: Sorry to hear that your card's dead.

Now back on topic:

For Vmem, a 100k should be fine. Just connect it between pin#3 and pin#6 of the up6101. Make sure it's et to max resistance before soldering it in.
You could also use a 50k poti if you don't mind a higher default voltage with the potentiometer at its max., but want more precision in higher voltage ranges. If you want both, precision and nearly same default voltage as an unmodded card, you can use 2 50k potis connected in series.

For VGPU: Ceemic already said it. Find alternative soldering points. It's not hard. Just use the meters continuity mode to find the right soldering pads etc.. If you don't want to use continuity mode, or your meter doesn't have that, just check resistance. Anything reading lower than 1 Ohm, is directly connected.

BTW: Continuity mode wouldn't kill a video card. The currents used for the continuity test are far too low. In fact it's just a resistance check that causes a beep when the resistance is low enough.