There's really no silver bullet for this, except maybe an RV with an air conditioner. There are simple things you can do to be able to sleep at least an hour or 2 longer.
Shade is probably the most important thing. If your tent is in the shade it will make a big difference. The next big thing is air circulation. I usually leave my tent wide open when I go to sleep, and use one of those O2Cool battery powered fans (which are not amazingly great, but they do help) in the tent doorway to draw air in from outside.
It will still get very hot, and you will wake up in a pool of sweat before you've had enough sleep. But, once you wake up you realize you're at Bonnaroo, so it's not so bad