On my last two trips, I tried to maximize my time at the parks during the cooler hours (morning and evening) and head to either the resort pool or the water parks in the afternoons. Also, Animal Kingdom has the most shade, whereas Hollywood Studios, with far fewer trees and much more blacktop, becomes a heat sink. It should go without saying as well that indoor shows provide some much-needed relief during the afternoon heat, and you rarely need to wait very long.
There is one unexpected plus to visiting in July, though. This is during the Florida rainy season, where you can expect a heavy thunderstom hitting during the afternoon fairly regularly. If you can wait-out the rain, the cooling effect of all that downpour can be significant and it lasts a few hours. Oddly enough, I've been more uncomfortable during a dry April than a wet July because of the moderating effect of the rain.