My RB button stopped working and as suspected, the plastic tab that pushes the switch had broken off. I didn't feel like waiting for a replacement part, so I decided to try something.
I cut the head of a nail, put it in my drill and carefully drilled a hole where the tab was. I cut another nail to size, filed down both ends and pushed that into the hole. It fits pretty snug but I did go all the way through so you can see it from the outside, but it works! And it probably won't snap off again