If they reduce the charge per-bid enough, then it does become an auction site. (And if it's large enough by that point, they'll still be raking it in.) They could also invite others with goods to sell and share the per-bid fee. If both of those things happen in a timely fashion, then it will be difficult for the authorities to argue that it's not an auction site.
If they are not charging for the bid (chance to win) but for the bandwidth when submitting a bid from the web page, then they get around this. They can demonstrate that by having another channel for bids, like email messages formatted Majordomo command-style.
Make this easily accessible, and it will be hard to argue that they are not an auction site. However, it can still be arcane (and slow) enough that the majority of the public still won't use it. Again, no one's gone broke underestimating the intelligence of the American public.
