Photochromatic rear view mirror?

I have one of these on both my Explorer and my wife's Forester and they are great. Both have a compass (hokey but fun) and eliminate night blindness from trailing a-holes with high beams. I can't imagine there is much to these and they are available for about $100 from the dealership and less on eBay and the local junky.

I'm assuming I have to tap in to a switched power line and make a ground, but besides, that the big issue will be attaching it to the windshield. Any suggestions?
 
Make sure it attaches to the winshield in the correct manor.

They make these (or at least used to) physically for mustangs, no fabbing or changing of the mount.
 
The stock mirror comes off with an allen key i think.
But the little mounting plate stays on the glass.

I have an explorer, and as for the mirror appears to be only connected to the glass, it actually has a bracket that connects it to the overhead console. A newer explorer (01+) may connect different, but i don't know.

I'd browse ebay for mirrors and see what is at least similar.