That particular shot is in fact much easier than it appears, and is very handy in situations like the one in the example. It's much easier to do when the ob is not frozen on the rail, and I've found that it's really easy for the eyes to misjudge the shot, and hit the rail too close to the ob and hitting it too full. This is just the way that my eyes see it, but when I'm trying to pocket a shot like that, I aim for a point on the rail that almost makes me a little afraid of missing the contact completely and resulting in a foul. With the ob frozen to the rail, I just can't pull it off with any consistency, but I have from time to time.
Doing this in a game is a blast to watch your opponents reaction 'cause in most cases he's sitting in his chair thinking to himself "ok, he can pocket the ball, but he's never gonna get shape."
dave