You can take a rachet style tie down...put in the middle of the tire and tighted it up. It will push out the side walls. I have done this before and it has worked for me
Fishmstr, we use to use ether on on our 38" truck tires. i didn't know a tire would bounce that high if you used to much. (word of caution don't try it under florescent lights that are hanging low) believe me, it makes a hell of a mess.