Btchance, I've never rented a wetsuit, but here are a couple ideas (although I'm sure you've already thought of them). Can you call some local stores (LBS might know of people in town who do it) in Memphis and see if they rent wetsuits? In your local tri community, is there anyone who could loan you their wetsuit for the weekend. That happens here often. We post on our local tri club message board. Most triathletes are more than willing to loan a wetsuit and are a pretty generous bunch. We borrow stuff from each other all the time (bike cases, wetsuits, etc).

Have a great time at MIM. I've heard it's a ball!