The only way I can think of getting to the lumbar support air cushion and pump is to remove the sear pad, and then remove the middle backrest insert. Both are only hooked/velcroed on but the hooks are really difficult to get to.
This thread has some pictures.
I would remove the middle seat pad insert first, then the middle backrest insert (hardest).
I forgot, the inner seat cushion is zipped at the back to the backrest outer leather (the one with side bolsters).
This zip is secured at either end by big staples which have to be removed, it is a bit tricky to unzip.
http://forum.a8parts.co.uk/showthread.php?t=6302