Working out. Seriously. I do my back excercises and sure it feels like a bitch at first but once I get on with it it'll loosen up real good. By the time you've done it a while your back will be stronger meaning you'll be able to do more with less back ache. My best mate swears by this as well because he had severe trouble with his back for months and months. I got him doing the same back muscle workouts as I was doing with weights appropriately tuned to his body. My theory is as well it eases the pain because it forces your spine in to the correct alignment and thus corrects your posture.