It's been awhile since I nested in a row. The comments above about using pillows and blankets to even things out are the most important thing to get some comfort going.

One other thing you can do: The seat belt anchors on either side of the seat cushion can dig into your back. Lift the seat cushions (they are only held in place by velcro) and put the seat belt entirely under the seat so that the anchors don't stick up. Keep one seat belt free down by your knees and throw it over your legs so that you appear to have a seat belt on.