Hmmmmmm....why do you have a rearview mirror in the first place? You really can't see anything out back using it, anyway. I pulled it down over 2 years ago. About a month ago I replaced it, and my stereo, and did this, instead:
Rooted Chinese Android phone (Zopo C2)....quad core, 12GB internal memory, 64GB microsd, FHD display (1920 x 1080) w/Gorilla Glass, camera shoots in 13mp, video in 1080p. It connects to my OBDII reader so I have real-time engine data, Google Maps + Waze, music, GPS calibrated speed, etc. I rooted my cellphone and it has hotspot capability, providing Internet connectivity for the "carpc". To keep it all stealth, I put a mirrored cover on it so that it flips over the screen when I park/want to go incognito. I tasked a bunch of the functions so that connection to my phone hotspot triggers a series of actions to activate apps/functions I want. A much better use of the space, IMHO. I'll be posting a write-up in my build thread over the next few days.
This works nicely as long as you have some of these: http://www.amazon.com/niceeshop-Univ...qid=1406819607 I picked some up for a del sol I had a loooooooooong time ago that had a horrible blind spot. Ever since that car, I've installed these mirrors on every single vehicle I have owned, including my M3. They totally negate needing a rear view mirror, at least for me.
If you need the mirror lights, that's nothing that a strategically placed LED strip won't fix.