I was just wandering this same thing last week! I heard a little taxi-driver-tip somewhere so I tried it: Just place a small pillow behind your back, resting just above the lumbar or midback helped me.IT HELPED SO MUCH! I am closer to the steering wheel so I can keep my spine organized but also my shoulders. My seat prevented it from rolling back and down since the cushioing was there. Not anymore! The pillow puts space between my shoulder and the cushion now. I also find that checking my blind spot is so much easier- I just brace my core and rotate. No more craning my neck with my shoulder rolled forward.

ill have to try the towel thing. i find that my cars lumbar support feels like its more like over extension. a towel mid back would probably help me out. for shoulders i tend to use the steering wheel as a form “bend the bar” to promote external rotation. once thing that really bothers me while driving long distance is my ankles/heel. especially the one i use for the gas pedal. no idea how to help that out… i find that when i drive with base feet its a little better then with shoes. but other then that not much has helped.