I was suffering the same with mine recently, so I had the exhaust off at the weekend to re-fit the whole exhaust.
I got the uprated rubbers from GSF, then put a big fat cable tie just a bit loosely around the rubber to take up the heavy pull if I'm giving it some. Now my exhaust is blow-free and nice and straight.
I looked at the powerflex bushes (but missed this thread!) and thought they were too pricey!