^ My first thought was to put a piece of black electrical tape over the mirror sensor...and then I realized how stupid idea that would be, as it would render your mirror in "dark" mode almost always!
Yeah, I can be pretty dense sometimes!
I've used (and currently still use, in my new Tribeca) the mirror's harness to get power for my SpeedCheetah GPS Mirror. This usually takes me a couple of minutes to play around in the car as I determine which pin slot does what, in terms of actually feeding uninterrupted but ignition-switched 12V power.
With that thought in-mind, I was wondering if you shouldn't just de-pin the two or three power wires feeding the mirror, and experiment with the final harness/pin combo that'll (
hopefully) allow the HomeLink and compass functions to still be powered, but will cut the power feed to the mirror's light sensor......