Shama said
In such cases I mostly stick to gentle rocking/circling/wiggling movements initially. Definitely no stretches. Then I would use energy techniques like mentally sending healing and relaxing energy to this part of the body or mentally talking to the lower back, asking it to relax and heal. This may sound weird, but I have solid case histories where this kind of method had very good results for clients with severe back issues.

Another thing which would probably work well is using heated herbal packs. This is easy to come by here in Thailand, but in the western world this is not so easy.  

Brilliant thanks Shama. I'll try that  if I can.  Hopefully I'll get the chance to treat him again before he goes back to UK.