I'm sure Mears would do this, but if you're staying off site and plan on doing theme parks, I'd rent a car. You can find great deals. In my opinion, you're going to find that using a shuttle from off site to WDW is going to be a real hassle and will take away from the magic of your vacation. You can get away without a car if you stay on site, but I really think you need a car if you're off site, especially if you're talking International Drive area or anywhere on I4.
Sorry if this doesn't help much....