chinchillas jump, thats what they do, eat, poop, jump..etc..... some may jump more than otherrs, but for curbing it , i don't know how you would do that.. some of mine jump out of their pen, so i don't use it much. you can use the bathroom, shut the door, close the toilet lid, take everything away that is dangerous to them.
you may also be able to get a cover for the pen, if not, look for a pen with a cover.
sorry, i know that doesn't offer you much hope..
jean