We bought two of these cushions to use for long trips a couple of years ago. They are clearly not inexpensive, but they are extremely high quality and super comfortable when used on the LS430 front seats. Wife and I drove 10 hours on Sunday with zero butt pain : ) I take mine out of the car and also use it in my Aeron desk chair since I am in that at least 8 hours a day.

The only caveat on these is they add about 1.5 inches to seat height so if you are tall it may not work.

http://www.relaxtheback.com/office-s...t-cushion.html

 

might have to try it