My suggestion to you would be to give up the reefer for a while. It sucks, I know (I'm currently clean for a little while), but it really is the best thing you can do. Substitution is a great method for folks that haven't been caught, and the testers don't know they smoke green. YOU, on the other hand, have been caught, and have been told by a nurse that you will take a month to get clean. If you pop up clean a few days later after having "unheard of" high levels in your urine, they're probably going to know something is up. You're already in trouble, and I'd hate to see you get in even more trouble. Reefer is amazing stuff, but it's not worth losing everything over. My advice to you is to quit for now, wait until you're back at work after being deemed "clean", and THEN worry about substitution.