I'm not an expert, but I did some more searching online and found that many people suggest putting your container in a box full of blankets or shipping peanuts, away from direct sunlight and air conditioning vents that might alter the temperature. Darkness also apparently help them keep from getting stressed. Personally, I would also hold him in my lap so I could be sure he wasn't getting too jarred. And remember to leave plenty of air. :)
Here's a link to another thread on the forum on shipping bettas:
http://www.bettafish.com/showthread.php?t=102500