Even 4 bikes aren't going to get close to the weight that will affect the hitch (actually the bumper that it's mounted to). It was SilverBullet (post 5 in this thread) that experienced that problem with carrying a jetski on his. I'm guessing that it was pushing 300lbs.
If he's not wanting to drill any holes then I'm guessing that he DEFINITELY doesn't want to take a box cutter to his cladding. He's still better off going with the Curt or U-Haul design.