Bump!
Thought about this, can any verify or double check this:
The dome lights are connected to the Internal Light Circuit at Pin 8 as shown in the Map mod (see signature). Wouldn't all you need to do is ground out that wire to the frame with a switch in there? If you were to just tap that wire, besides turning on the light, what else would that trigger: door ajar warning light, key hole light...? Not knowing what else that would trigger I thought about also adding a diode down stream of the tap so other functions wouldn't be tripped.
Hopefully that stirs the pot for the minds.