I have a 2011 North Trail 26LRSS that has an extendable rear bumper. On this bumper is about a 3' post that will stand up and lock in the standing position. I've been told this is to secure bicycles to. For the life of me, I can't figure out how this works so as to keep the bikes secure without either damaging them or simply having them fall off the bumper tray. It seems to me there should be an accessory item to carry bikes for this setup, but I haven't been successful in locating anything. Any ideas?