I would assume if you knew what you were doing with a router and template you could use the pickguard to make another without the P pickup hole. Then use a template of the humbucker pickup to cut an appropriate hole in the pickguard, put it in place and then use that as the template to route the body to the correct depth. That's how I would go about it. Or if the humbucker is bigger than the P pickup hole then just use the provided pickguard and cut that etc.