Well, everyone who creates a feedburner feed has to manually approve the name. In my mind it would be a simple substitution. If the user adds a feedburner URL for a specific forum use that. If not, use the autogenerated one.
In my case I have one FeedBurner feed for the main external.php RSS 2.0 feed. Instead of
www.myforum.com/forum/external.php I want it to use
www.feedburner.com/MyFeedName