I have the exact same problem. In December '09 I took 415 for a ride and destroyed my lower back. Same diagnosis from the Chiro.
I didn't do any sort of therapy for the first year (probably should have). I started up Chiro a few months ago and did it for about a month. My mobility increased a bit, but the pain was still there.
Recently I started doing a few different yoga stretches on a daily basis (as per the article on this site "Yoga, Yes Yoga for Big Bastards"). It seems to make the pain almost entirely disappear at least for a limited window of time. I do them before and after training. Seems to be working a lot better than the Chiro.
All in all though, I'm quite sure this thing will be bugging me for the rest of my life. The yoga is making it much more manageable.
I read your post and see that you have been practicing lots of different rehab techniques... Thought I would chime in anyway on the subject. Who knows, you may find it works well for you too!