I think you have three options.
1. Strictly enforce the rule of be a member or do not compete. Kinda harsh aint it? It can do more damage than good in the long run, pushing people away will leave them bitter.
2. Be lenient and do not enforce anything, if they win then make sure they are members. But then its a catch two because we are not enforcing the rules.
3. Leadership - My favorite. if my subordinate fails I have failed him. A good leader makes sure his people are setup as much as possible to be succesful. If I were area rep, I would start tagging folks early on. I would surely get in touch with the regulars who have a chance at winning the event. I would make sure the top 10 teams are registered and all their paperwork is good to go. I would then work hard on the rest to make sure they show up and give them all the options available.
I keep hearing you guys talk about "my chances of winning the event". I think we would see 3 boats at any regatta if we placed that much value on getting on the podium. Is that REALLY what you guys think the AC eliminator is about? Really?
At the end of the day, it's actually quite an interesting, though provoking, and challenging way to race when you commit yourself to racing an entire fleet on portsmouth handicap. The conversations, the opportunities, the fresh change in strategy (covering a guy you owe three minutes too doesn't help you). It's a freaking regatta. If winning is everything, I expect to see all your boats up for sale effective immediately.
Lastly, you don't have to cater to "the guys that have the best chance of winning". They can play or they can choose not to play. The event is the North American Multihull Championship and whoever wins it has won it regardless of who's name was or wasn't on the roster.