This grip I first place the 3rd finger along the seam and make sure the majority of the finger is in contact with the seam and then wrap the rest of the hand around the ball almost gently. Admittedly it needs pictures so I'll work on getting them shot and uploaded to the Flipper blog listed below. The other keep aspect to this ball is the release. I probably still have a tendency to naturally bowl out of the back of my hand and I'm convinced that when I release the ball my thumb is coming so far round anti-clockwise that I'm beginning to bowl Top-Spin - moving towards Off-spin. In order to correct this I have to concentrate and make a concious effort to turn the wrist so that the sensation is that the hand comes over and into the release position with an emphasis on it feeling as though my hand is erring towards an Karate Chop feel. If I do this I feel the ball come off the 3rd finger with definite emphasis and contact and it spins like the big leg break. I was pitching these well outside of leg and they were turning into the stumps. It'll be a long time before I try that in a match but it looks promising.
Recent videos that I've uploaded in conjunction with a bunch of new blogs that I'm working on include this series which explain the variations of the Flipper. Most of these variations are extremely rare and have been lost to the 1930's but if you do your research and read through the books by Clarrie Grimmett and have an equally obsessed friend (possibly more so) who's in NSW Australia and has access to the libraries there you can re-discover them.
These are all in conjunction with this new blog which deals with the Flipper. http://spinbowling-flipper.blogspot.com/