I have worked with and helped a few people to correct the issue completely. This is a tricky subject and can only be programmed after a thorough assessment of the individual while working with the clients Doctor and or Physical Therapist. No two piriformis cases have been the same in my experience. I would ordinarily stay away from this type of training but having had sciatic issues in the past and I am intimitaly familiar with this problem. With that being said I cannot give direct advice to piriformis syndrome in general, but however will recommend a good book… The Wharton’s Back Book.
It would be a good idea to check out, it is a great resource.