First off, don't sweat it
It is hot, but it is manageable. I think you'll find that the crowds are decent at that time. If you haven't made your ADR's yet, make them NOW.
Keep hydrated, that is the number one thing. We carry steel water bottles, and sugar free flavor packets from Wal Mart. We ask for cups of ice water at the CS locations (it's free) to fill up the bottles, then pour in the flavor and shake it up a bit. If it starts to get too warm, we ask for a cup of just ice. We make sure to always have a drink in the bottle. As soon as one of our bottles is empty, we stop for a refill.
Beyond that, we use touring plans, and try to do most of our planned touring in the morning hours before it gets really hot. Later in the day, we try to take it easy, take advantage of air conditioned shows, and longer rides like Country Bears, Haunted Mansion, COP, The Great Movie Ride, and Festival of the Lion King. We usually have lunch at a CS with indoor seating, and take our time, perhaps an hour for lunch.
If we are getting tired, or hot, we find a spot to sit down for a bit, have a snack (perhaps an ice cream) and a drink. A bench near one of the play fountains is a favorite spot to rest, as DS6 can play in the water, and the rest of us can rest a bit, and cool down.
Supper is nearly always a TS, and again, we take our time. We always allow for at least an hour and a half in our schedule for supper, so we can really rest our feet and legs, and cool down.
The afternoon parade is a good chance to rest a bit too. Make sure you have a cool drink, and find a place to sit in the shade for the parade. Even though you are still outside in the heat, the shade helps, and just sitting, and having a cool drink goes a long way.
Be prepared, and you'll do just fine in the August heat!