I try and do at LEAST 5 minutes of yoga a day-which, I know seems like an impossible feat during a flare-up-but believe me, it has taken down my pain levels so, so much. What I recommend for everyone is finding a partner/buddy to do it with-that way you can keep each other motivated. I used to not even be able to lift my purse for more than a few minutes, but since I've had the light exercise/stretches, I feel like the Incredible Hulk in comparison, hahah.
Also, y'all should try the Wii fit, it's fun-its a very amusing way to help yourself, though I admit when I'm having a "good" day it's difficult to not want to go overboard and work out the way you used to pre-FM..
Hope that helps, good luck and keep us posted on how it works for you!