before i got an exhaust, my stock exhaust was a lil off-center for my kit's rear valence as well, i used some plumbers tape, like a roll of metal that has holes in it, it's pretty soft... i wrapped it around the exhaust pipe and the rubber hanger, when it was tight enough i used a short wood screw and bolted the strip down to the rubber hanger... it held up fine with no noise or slipping for the 2-3 months i had it on...
i think it's a good idea to mod off the rubber hanger versus making a solid mount, my new exhaust bolts to the tow hook mounts and the muffler shop that did it used pretty thick rubber grommet/washer between the mount and the chassis, but sometimes usually when i let off the gas at speed the pipe will still vibrate enough to cause a short tinny buzz...
