Routesetter.com teaches how to stop climbers from using the bolt hole as a mono in the gym. At first I thought this was humorous, then I remembered how many times I’ve seen climbers try using them as pockets (especially those with tiny fingers).
1. Take a two-foot (or so) long piece of standard issue setting tape.
2. Loosely bundle the piece of tape into a cylinder-shaped ball that is longer than it is wide.
3. Stuff it. Shove that ball of tape into the offending bolthole. Be careful not to pack it in unless you never plan on moving the hold again.You may have to put more tape in the hole to fill it up. But using one single long piece will make it much easier when its time to get it out. Try to make the tape flush to the holds as best you can.
Check out the article for pictures on their steps. There’s also a nice follow-up discussion in the comments.