I'm glade you're not designing office furniture or car seats for a living. Take a good look at the Aeron chair. High end car seats have lumbar supports. How many g-forces happening in an office? Like i said before ; why pay for something your not using...
g-forces imparted to the driver are overwhelmingly lateral; not longitudinal. Lumbar supports are not to alleviate g-forces. Correcting posture while driving keeps the driver alert.