JKnight
(Keeping SmartThings limping along since 2013.)
4
In my testing, I discovered that I could just short out the button switch on the circuit board of the wall mounted button with a cheep relay turned on for 2 seconds (simulating a momentary press). On my MyQ opener, the wall mounted button sends some digital code or encrypted message via the two wires to the opener, so connecting anything directly to the opener was not an option.
Here is an example of my setup connected to a dumb garage door opener, but you could modify this and connect the relay directly to the button switch on the circuit board of the wall mounted button.
I recommend combining this with a camera, and perhaps other sensors, in the garage to mitigate some of the other concerns that have been raised.