That can be a little tricky. How do we know it is FACET pain and not a strain, or arthritis or something else? Had he fractured it before? What is causing the pain/what is history/what makes the pain worse, etc etc? Has he had X-rays or MRIs to make sure its not stenosis or bulging disk, etc.? Because some conditions require flexion strengthening and some require extension strengthening.
i would ask for a little more info and decide based on his responses.