I have a 2004 K12GT. Fortunately, it came with a passenger backrest. For the passenger to hang on, however, I use a black (24", I believe) EPDM bungee strap looped around the seat just behind the raised portion (in front of the passenger) and hook the metal S-hooks together under the seat. It's a rather cheap, but elegant solution (if I do say so myself) as it's strong as heck, but gives just enough to get fingers under for a good hold. Plus, it blends in well with the seat and is weatherproof. Only problem is that the hooks interfere with getting the seat on easily. Next time I remove the seat, I'm going to also remove one of the strap S-hooks and thread the end of the remaining hook thru the hole on the other end of the strap. That will cut down on the added thickness.