Could you place a small amount of epoxy on a broken plug, screw it back in and let it cure then screw it out?

 

Actually, part of the service procedure is exactly that. But for when the ceramic stays in, use take a piece of electrode wire and expoxy it to the remaining ceramic and you can pull it out after you tap it. I'd be worried about pushing the plug further in, but it would be worth a shot in order to save having the head removed!

 

I was talking about the gel type epoxy (just a small amount) to basicly glue the 2 pieces back together.