I agree with some of the advice given so far i.e ensure that hip mobility is adequate to ensure the lumbar spine is not the site of compensatory mobility. Ensure that you also look at combined hip movements and rotations as these are functional movements. How aggressively you decide to mobilize the soft tissue depends on whether you feel the hip restrictions are myofascial or capsular as different techniques would apply (the most effective way to decide how to mobilize myofascial tissue is always up for debate and some may say that bruising implies excessive force while others may not).

Secondly tell us more about HOW the patient flexes and extends not just whether there is pain i.e the lumbo-pelvic-hip rhythm e.g excessive lumbar contribution with late hip movement and also whether there is any hinging/kinking at one level with extension (be sure to rule out segmental instabilities as Mckenzie extensions may aggravate this). If you are using the McKenzie extensions to treat a 'derangement' pattern using centralization procedures than I would agree that mobilizing neural tissue in a flexed/slumped position may be contradictory to this. Although hamstring stretching may be a good idea be sure you are not aggravating the neural tissue as mobilizing/desentizing neural tissue may require a different approach than regular sustained hamstring stretching. Be sure to make sure the thoracic and thoraco-lumbar spine is adequately mobile as this wil also aggravate the lumbar spine and of course make sure as always that there is adequate core stability.

E Huner PT, FCAMT