I haven't done this myself but you could try to wrap youtube code around div and then make a script that allows 1 click but after executes void(0); or something when trying to click in that div. Now I have no idea if this actually works and I can think of few things that might prevent it from working but it was the first thing that came to mind

*edit* Yeah and with that suggestion you effectively disable user from using player controls

But if you want to go hifi, you could just do "allowed click field" based on pixel coordinates and that way make the bottom 20px clickable and the rest you can click only once.