There was one SPECIFIC one, that when I felt the pain, and if I did it, the pain would virutally go away INSTANTLY. Now you're supposed to do it regularly, like 3-4 times a day, but I was lazy, and I would sometimes just doing it when I felt the pain, which is NOT what you're supposed to do, but it did help me. Now i'm not sure 100% if it will help you out, but it is worth a try, if you are feeling the pain, really bad, then just try this one. I'm gonna try and find the direct link to the exercise...
This is the page about the sciatic, you probably already read it...
http://www.back.com/symptoms-sciatica.html
This is the one that I tried, and it helped (specific for stretching the piriformis muscle)...
Piriformis Stretch - Lie on back with both knees bent. Cross one leg on top of the other. Pull opposite knee to chest until a stretch is felt in the buttock/hip area. Hold 20 seconds. Relax. Repeat 5 times each side.
Here is a the site, scroll down, near the bottom, you will see the video you can watch, the guy shows you how to do it...
http://www.back.com/articles-exercises.html
Good luck,
Let me know what happens.
T.