No two 'back pains' are the same so what helps me may not be for you. That said, the no racking point made above made a huge difference for me as well. Often in friendly games I just spot the break and play 'rack your own' to avoid it. As for actual playing adjustments, adopting a more upright stance helps. Personally, I like playing low to the cue with my head, but can somewhat mimic some aspects of an upright stance by bending both knees and lowering myself straight down into my stance rather than bending from the hips. Dropping straight down not only decreases strain on the lower back, but is also a great way to get your head in the right spot as you are sighting a ball standing and then maintaining that head position relative to the shot line as you get into your stance.
Also, no big stretch shots. Just get comfy with the bridge.
Away from the game, core exercises help back issues tremendously. You just have to find a routine that doesn't aggravate your back and make sure your technique is spot on. Though really, even if it isn't at first, an ab workout for people with bad backs should pretty much be a mandatory part of their daily routine. Doesn't take long and saves you a lot of pain....at least it has for me.
). Your belly will push out on the breath in and then when you exhale you tighten your stomach muscles and kind of force the air upwards like a toothpaste tube. It's a silly way to explain it but filling your lungs with fresh air and expelling them as fully as you can gets rid of a lot of different muscle tension problems.
