Oy!!! Try tying him to you with a leash and watching. When he starts to sniff take him out. Also, if he pees and wants to come back in, then maybe go out and throw a ball for him for a few minutes to see if you can get the "juices running" so to speak. Sometimes, it seems to me, activity will trigger them to poop.
Another thing to try is a door bell. I mean the kind you just dangle from the doorknob. Every time you take him out, ring it before you open the door. Then if he rings it, take him out even if he just wants to play! The first time he TOUCHES it, take him out. You want him to get the idea that if he wants out, ringing the bell will cause you to open the door.
You can also try going back to basics with the crate but I think I would go for the above options first and see if he gets it.
Good luck! They are a challenge aren't they?