Lichelle Marie has an awesome technique:
http://glamagic.com/free/bangbrosnetwork/movs/013-lichelle-marie-and-friend-fucked/libraryofthumbs.html - vid #3
http://juggs.butchermovies.com/bgb-lichelle_richelle/03_mkfr/index.htm - vid #1, my all time favorite, that's what ballsucking is all about :D...