Make sure you don't blow a fan or anything directly on the cage. Breezes or drafts can chill a hedgehog and cause hibernation or colds.
I believe one of the easier methods I read was to get some of those blue plastic ice packs that you can freeze, and if it gets too hot in the hedgehog's cage, just place one of them on top of the cage. The cool air would sink down into the cage and cool it off. Just be sure to monitor the temp carefully.
Another thing that I liked and copied, was drpepperheather put a ceramic tile in her hedgehog's cage, so if he got hot, he could splat out on it and cool off. I thought it was a great idea, I got a marble tile for Lily's cage.