I was always told (in the military) that traing your abdomen is also a good way to prevent all kinds of back pains. This, because the muscles in the abdomen can then take over from sore muscles in the back. From that point of view, it wouldn't be too big a jump that those front muscles also keep discs further apart and relieve that type of pain.
Sit-ups (done properly!) is usually the easiest accessible method, but if you have the option, take up swimming in Olympic size (or half-sized) swimming pools. Or much smaller swimming pools which have a system in place that generates a variable current. The same concept as a treadmill for running.
Swimming is good as it provides a full body workout, but without the impact on the joints you use for running. Your buoyancy relieves much stress on painful joints and Swimming builds up muscles, which relieve pain even more. 100 Meters swimming should compare to a brisk walk of 2 kilometers or 5 kilometers of cycling at normal speeds. In a pool of sufficient size it hardly matters if you "cheat" by using your legs to push you off.
I have met lots of competition swimmers and water polo players. None of them complained of back pains and even in later stages of life, most were able to keep up their youthful physique. Just saying that swimming is a good way to keep the whole body in shape, without putting stress on your joints.