Originally posted by ElJamoquio This is a common flaw. Some people have glued theirs back in; you should be able to search for it (sorry, don't have a link).
I used a finishing nail, myself, in the interim.
Ditto on this. The button fell off of my K-x (never to be found), so I cut a nail down to size, nestled it through a trimmed piece of a synthetic cork from a wine bottle to keep it from wobbling, and then put some clear packing tape over it. Works just as well as well as the button did, if you don't mind the kludged appearance, and saves the need to disassemble.
Not sure how you'd retain the weatherproofing, though... quick spritz of Rain-Ex?