On their heals? 
I thought you're supposed to hit their butts down, that's why you need the cardboard in place between the legs and the torso.
Keep their wigs on,
bend them with the cardboard slid in between the legs & torso, place their
heels against another piece of cardboard on the floor, take a
towel & cover their head & wig, next smack down on the head. Be careful with the Klicky's with boots that are glued from factory, they may snap off needing to be reglued.