So I was watching the DVD special features for season 3 on the bonus disc and in one of the sections (I think it was called "Lost in a day") where they take you through what happens in a whole day in Lost, there's a part where a man is trying to figure out how to get the arrow to go through Charlie's guitar. This man has long hair and a goatee, and is somewhat baldind. The moment you see him you will realize that he was the man sitting in the chair playing Jacob. Now we know they haven't cast Jacob yet but I'm certain that this is the man that is in episode 3.20. He is some sort of crew member and obviously not an actor but all they needed was someone to sit in a chair for .2 seconds. I don't know how to get screen caps or anything but if someone does, be my guest.