Pretty sure the rubber ball will mainly work for your cheeks. I would imagine people with a drop between there mouth and cheek bone would love this over puffing their cheeks up. But if it's your jawline your after... try pulling the skin up towards your nose. I have to pull fairly hard to get my jawline but it works ^_^. Might want to lessen the angle a bit too while the skins taught sin it won't have much give with all the tension - easier to cut >.<.
Good luck, and great story. Not sure if I'd stick a ball in someone drawer in my mouth but hat's off to that dude.