I saw this in the blue room a long time ago and decided to do it since I only have one garage door opener and it is in my wife's car.
I started by ordering a home link device from ebay. It was cheaper than a garage door opener.
Then I removed the driver's side AC vent panel. This comes off easily with a firm pull towards you and up a little.
It only has four clips holding it in.
Then using the plastic cover for the buttons as a template, I used a dremel tool to cut out the 3 holes for the buttons and drill a hole for the light.
I then used double sided tape to affix the home link device to the back of the panel using the panel to hold the buttons in place.
After splicing the power in and attaching the ground to the bolt behind the vent panel, I reinstalled the vent panel to the dash.
All I have to do now is test it when my wife gets home. I forgot to get the garage door opener from her car before she went out. I will add the results as soon as I can.