...and that makes me unhappy, too! I've searched like crazy and cannot locate the detailed thread describing how to remove the passenger seat, undo the upholstery, add foam to seat bottom and back, and re-install. I remember reading it a while back and now regret not bookmarking it! We drove for 8 hours and her butt/legs were very sore. Admittedly we are getting older (58), but I'm hoping to resolve her problem by doctoring the seat with a bit more plushness. I am fine, but she is not. BTW, she is 5' 2" tall, and in pretty good shape. Thanks!
Just a word of caution, the seat has an airbag sewn in, so be careful when messing with the inside. I would recommend looking for some kind of external seat crushion instead. Some folks at work have those on their office chair. I imagine you can find them at Office Depot and try a few different thicknesses, etc.