How about parking in the Festival Bay Mall parking lot, hiking out to International Drive, crossing the multi-lane road, catching the I-Ride Trolley going south and getting off near Wet n Wild, crossing the multi-lane road again, and having fun at the water park?
It seems like a lot to go through to avoid the parking fee but I'd think that Festival Bay (or one of the smaller outlet shopping center parking lot across the street) would be one of the few spots along I-Drive where you wouldn't risk being towed. It's about a mile and a half to two miles from Festival Bay to Wet n Wild.
Good luck.
Dick Taylor