Same problem! I put clear mounting tape on the back of the button and stuck it back on.
http://www.amazon.com/Scotch-Heavy-Duty-Mounting-Clear/dp/B00004Z4BU
Tried super glue, but it was a mess.
In one case, I had actually lost the button. I found a picture of it on the internet, printed it at the correct size (took some experimenting), laminated it, then trimmed it and stuck it on with the tape. Looks fine from a couple of feet away.
Bob, April 2015