I was looking at a thread on another iPad forum and members with a similar problem have reported that Apple has replaced the back or swapped it for a new one. No harm in seeing what they can do for you; give 'em a call or better yet, drop by a store. I'll PM you the link to the thread.
But I'm not sure if there's any quick remedies like there might be for a car dent; I haven't seen any, unfortunately.