Might be useful:
https://www.youtube.com/watch?v=lbQgha7xudw
http://www.autostraddle.com/happy-in...ng-day-201101/

I have tried it, and done it to others, and it is something you need to learn. Lots of lube, take it slow, take your time. When it works, it is just awesome, the most fantastic energy waves back and forth. But you do have to learn it.