Several .orgers are looking at doing this too. Read this thread =
Adding Footwell Lights
= for a discussion on adding footwell lights. Look at how the mirror lights are switched. Using LED's is the better way to add the lights, additional load, to the comfort module. I haven't found a good color LED to use yet. The whites are still too blue for me. Keep us posted on your progress.
I plan to tackle the wiring method this spring. Lights installed, but using a (salvage yard donor) rear window defogger switch to turn the on and off now. Good luck.