Maybe I don't know what I'm talkin about, but I'm gonna throw this suggestion out there anyway: how bout anti-seziure meds like Neurontin? or myofacia meds like Lyrica? I don't have back issues but I do you impinged nerves (tendonitis & Thoracic Outlet Syndrome) and I have used both of these in tandem with opiates (kid's stuff compared to what you got goin on tho!!) for pain management.
Just a thought. Good luck!!