From the Twister Side Control you can transition to N/S and grab and Arm Triangle on the way. I mentioned this as an option when you are going for the Nutcracker Submission.
The guy in the video goes through a bunch of little details at the beginning of the technique. When it is all said and done he is basically going from Twister Side Control, trapping his opponents arm and then transitioning to N/S.
As you transition your back and hip are going to trap your opponents arm. In the video the opponent stays flat on his back and the guy finishes with a Gable Grip.
I have found that as I transition the person will end up on their side as they try to escape. When this happens I Triangle my arms so that one of my forearms is under their neck and their trapped arm is pinned to their head under my chest. Then to get the tap you squeeze the Triangle and drop your chest down to the floor.
