How to cork my baseball bat?

Ok so i originally wanted to cork my wooden baseball bat as a joke for those pick up games with all my friends and neighbors. you know as a joke to hit it far. ( not to use in a real game) but i discovered it was to hard to drill a hole intoo my wood bat so i decided to use my old metal baseball bat with a 2 1/4 in barrel.and i wanted to stuff tennis balls in there.... but the tennis balls are way to big! any ideas of what to put in it? and where should i get it from????