This time of year you do not need a hot pack! I've received snakes via UPS from Reputable Big-Name Breeders, so it can be done, even though I think it's technically illegal, and could be dangerous for the snake if he's caught in transit. Fed-ex it's possible to ship snakes legally, but in the US they makes us go through several months of hoopla to get "certified". And I think there's also Delta Dash (airport to airport?)
I think the easiest would be if you could use Ship Your Reptiles dot com.
You want to do it overnight. The longer he stays in the box, the greater the chance of something BAD happening to him---like being left out on the tarmac at an airport to roast in the sun. And stress is a health hazard, too.
Otherwise I would seriously consider finding a reputable breeder in your area who IS certified to ship, slipping them $100 and begging them to take care of your little guy for a week before shipping him to you.