UPDATE!
Sorry it has taken me so long to get back to you, but I thought you would like to hear how things have been going with this guy.
Thank you so much for all your helpful ideas and suggestions - they have been invaluable. Having a wide variety of treatment options available helped build my confidence in my own abilities and as a result, my patients confidence and belief in helping himself.
I used Mulligans techniques to increase lumbar flexion ROM, taught pilates type exercises (partly based on those you suggested and partly on those I have learnt myself at classes) with incorporated upper and lower limb movements. I also went with him to see him in the gym, where it became apparent (despite my lack of experience in this area), that his techniques were poor and he was putting a lot of stress though his LS. With the assistance of one of the experienced Personal Trainers we were able to work on this and develop a more suitable gym programme.
As well as this, I found that he had been spending a lot of time during the day sitting slumped in a fork lift which had been aggravating his symptoms - simply using a rolled up towel helped with this.
Overall, he has reported a 90% improvement with his symptoms, and importantly has incorporated the "pilates" exercises into to his x3 weekly gym sessions.
Sorry for waffling on, but I am so pleased with the results I just wanted to let you know! Thanks again for all your advice and time, you are incredibly kind.
Many Thanks,
Catherine.