You could grab the check from editpost.php and use it in showflat.php and showthreaded.php around the "Rate this topic" section. That will allow only the creator of post and admins should be able to see it. Of coarse, that is not a total solution, because if someone clicks on their reply to view the thread, I think it will still show up, and I think that it would still show up for replys in threaded mode. But, that is a place to start at least.