You can cut off the four bumps with a knife, there will be a metal membrane in there that you can clean with alcohol, reassemble, superglue the four holes with a toothpick, just do it outside as the fumes can go into the membrane making it a little bit non galvanic...
For GBA and DS shoulder buttons, and megadrive pause buttons, you can usually drain them in alcohol and klick like a freak to make the oxides and other residues go away.