Was just going to start a thread about this. The only thing we need to find out is when a light comes on is it because it is given 12v or because it's given a ground. For example when something trips the check engine light, does our computer send 12v to that light or provide it a ground hence illuminating it?
Considering there's only one ground wire in the harness on the back of the gauge cluster, I'm assuming that each light is already grounded, and that it's given 12v when it's time to light up.
If that's the case, the Haynes manual spells out what each wire is for, so it would be as easy connecting each dummy light wire to an LED and then using all aftermarket gauges. This is something I planned to do next winter.