I was able to add lumbar support to my driver's seat by removing the hard plastic seatback panel (2 screws), and inserting a rolled foam support between the foam of the seat and the vertical wire seat support. You'll see what you have to do as soon as you remove the plastic panel. For some reason, it was almost impossible to re- install the two seatback panel screws until I greased them.
My back thanks me everyday.
Good luck.
Marvin Stockman