You have th basic idea. The only difference is with your inside leg, don't shift it back, try to imagine you are trying to squeeze the girth itself. If it helps, imagine your leg is the pole he is using to turn himself around, like when you were a kid and grabbed a light pole with one arm and swung yourself around :-) He'll use that leg as his 'support' where as your outside leg will keep his ass from flicking out :-)