My brothers in the same predicament. From what I'm hearing the VA is beginning to look at this more realisically and some VA hospitals are looking the other way on MJ use. One loop hole tp keepp in mind is to talk to your VA doctor and see if he will prescribe you Marinol. The VA can legally prescribe it. Then you can try all the different strains of cannabis you want.
In the case of my brother he just gave up and continues to live in severe pain.