Clear LiteRumble history
You should be able to delete the data from the AppEngine web console. Otherwise you can simple make the clients upload to a different named rumble, and the old one can be for the demo/setup bots.
I have tried to remove the data from the datastore by selecting all database entries and delete them. But the data on the webpage is still there, so the data must be stored somewhere else. To create a new rumble seems like a annoying workaround :)
There may still be a copy in Memcache - if you clear Memcache and the datastore everything should be gone.