Part of teaching stay is teaching a calmer state of mind.

A dog cannot stay for an extended amount of time if s/he's mentally bouncing off the walls. So to teach an extended stay, you should be doing it frequently and in a very quiet area with low distractions. You really just have to start with baby steps. Every time Joey gets up, just step forward into him and repeat until he starts getting some self-control. You might have to do this 20 times the first day. But the second day, you'll only be doing it 5 times. The third day, you'll only have to do it once, etc. etc.

But, yes, a clicker could definitely help! A clicker is so wonderful because it's crystal clear to both human and dog, and I certainly think it facilitates more efficient human-dog-communication.