I think the fact that he still gets pain in his lower back after a prolonged standing is still cause for concern, this is not normal for most people. fatigue could be an issue with him so as sdkashif said endurance and also core work might work well with this chap. get some TA activation and pelvic stability into the mix as well as mobilising through the region. doing fascial work though a hypertonic psoas can often give great results when treating chronic LBP. Squish, stork, active extension whilst prone and trendelenberg should give you a general idia of his hip stability and any restrictions or imbalances within the lumbopelvic region. put him back in the oven, this guys not done yet!!!