Yeah lots of breeders in the states use the popping technique. They also probe too. There are a number of you tube vids showing you in good detail how to do this. All you have to do is do a search for popping.
I've used this method (popping) quiet a bit, it's a very good way to sex hatchlings. It does take a bit of care but once you've been shown it's pretty quick and accurate. I wouldn't recommend using it on adult snakes though, they have far more muscle mass and I think there's potential for injury.