I buy a few pounds of cherry plums and regular cherries every year and make bounce with them. The cherry pitter is worth the investment for both, believe me. THe coke bottle and chopstick method got old real quick. Worth has a great point though, especially with the really ripe cherry plums, you probably wont salvage all of the flesh.
All the more reason to drop them in a big gallon jar, add a few cinnamon sticks, maybe some sugar, and fill with your favorite alcohol. Cherry Plum Bounce....oh yeah.