Its a very common problem now. Know of a couple people dealing with the same issue. Yes freezing urine will work. Take about 2 months of being MJ free, then gather as much urine as you can for freezing. I would pickup some of those 2 or 3 ounce travel bottles of shampoo, flush thouroughly and then put your thc clean urine in them. And practice with one othe bottles with just water in it to keep your heat right. Its a shame that even in states where MMJ is a completely legal prescription that you have to go through this.
To try and spred up the getting clean change to high fiber diet with metamucil and try to exercise as much as you can.