Hmmmm. Maybe just spend some time hanging out in the car without driving it. Let him jump in and out of the car, have a nice blanket for him to sit on, you could even feed him some meals in there. Then drive around the block, stop and treat. Etc.
I know what you mean about them trying to sit in your lap while driving.
I finally got Thor a booster seat, so he's strapped in, AND now he can see out the window.