Lower back stuff is a pain. I've been dealing with a chronic pain for several years now. Of course, it is not a joint problem, just muscular.

I would think that things like good mornings and RDLs would be ideal as the primary movement is across the hip joint, with little flexion of the back. You know, as soon as you are in position your back stays locked. I would imagine that hyperextentions would be more troublesome since that would have you flexing your back.

Ever try reverse hypers? I have ideas about how you could probably accomplish these even without a reverse hyper machine (which is the one machine that I would buy for my gym, without a doubt. Even though there is a lot of spine flexion in a reverse hyper it seems to also work as traction, and allows the spine to decompress.