I would start with putting him in a harness that doesn't allow him to run around. Then don't go anywhere, just sit in the front seat and calmly say whatever you do when you want him to calm down, like "easy". When he calms down (which might take a bit so bring a book or something) then give him a treat and say "good boy".
It's going to take time to train him but it will be worth it. He'll be much happier and it will be safer driving with out all the ruckus in the back.
