Dollar and Thrifty appear to have the same rates at MCO (I don't know if they're officially dual-branded there--i.e. in the same building--or still maintain separate operations), so you might want to try booking with Thrifty and using the Orlando Magicard discount code, which waives the additional driver fee. (Technically, you'll also need to order the free Magicard itself from the Orlando/Orange County Visitor's and Convention bureau here.)

That same page mentions that the Magicard also has a code for Dollar, but it doesn't mention waiving the additional driver fee, and I can't tell you definitively if it does or doesn't.