While looking for a built in garage door opener, I came across the Flash2Pass, from http://www.f2ptechnologies.com/. I found a kit on ebay for $59. After installation, you flash the high beams twice and the garage door opens/closes.

Advantages:
Inexpensive (Relative to homelink mirror)
Convenient (Activates from light control on steering column)
Stealth install (Interior is unchanged)
Simple installation 1hr max (About a 2 on a difficulty scale from 1-10)
No cutting the headliner
No modding the dash
Works with any opener
Uses rolling codes, for security
Requires no real electrical knowledge. If you can point to your high-beam bulb, your there.
Easy to move to a new vehicle if you buy a new car.

Disadvantages:
Your lights flash (Some worry that their neighbors might be bothered at night)
You have to relocate the receiver if you move. (Probably easier than finding the instructions for reprogramming your remote though.)
Only operates the door (Electrical gurus might disagree)
Cost - (Relative to stealth mounting your current opener)

Here's what I did:
1. Find the wires to the passenger side high-beam and cut back the black cover a bit to get access. Mine were white-black and red-black.


2. Place the end of an included Posi-Tap connector around each wire.


3. Screw the body of the Posi-Tap onto each end, piercing the wire.


4. Unscrew the outer end. Put either of the wires from the F2P module through the end. Screw the end back on to the body of the Posi-Tap. Repeat for the other wire.


5. Clean the side of the passenger side headlight with alcohol. Use 3M mounting tape to attach the F2P module to the side of the headlight. (There is a nice little ledge to hold it btw.)


6. Use included screws to attach the receiver to the wall in your garage. You can either replace your current button or mount in parallel with your button, attaching a jumper wire to the same place on the opener where you button's wire attaches. I attached high and in parallel to get max. range. You probably should unplug the opener, while installing, to be safe.



Done! Mine works at the stated max range of 75 feet and sometimes about 10-15 feet beyond. Each receiver can work for 6 transmitters, if you are lucky enough to need so many. After using it, I prefer the F2P to my wife's homelink, because it is handier. On hers, I have to reach up/over to the mirror and hold the button for 2-3 seconds.....awkward. If you move F2P module to a different car, you can just unscrew the Posi-taps and paint over the tiny hole in the wire insulation with clear nail polish.

 

What if we have HID installed?
Love the concept.

 

I think that the majority of people with HIDs only replace their low beams, because of the turn-on delay. The high beams would be unchanged. Either way, the factory high beam wires would still be present and functional.