That is so cute! My boy does the same thing and he always sits in the driver's seat too. I have a gate to block the back of the little s.u.v. I drive to keep him in the back but he's figured out how to get around it. When it's cold out I don't mind so much, he keeps the seat warm.
btw- on a more serious note I was chatting with GSD owner/breeder/trainer a few months back and she told me an aggressive behaving man approached her car as she waiting to pick her daughter up from work. He got within a few feet of the car, her female GSD poked her head out of the window gave him a loud warning bark and he took off. She feels her dog prevented a possible car jacking attempt!
"Mommy, that was a real dog driving that car!"
"Timmy, that is rude! You shouldn't talk about people like that!"
"No, mommy it was a real dog!"
"Timmy, when we get home, you go straight to your room and stay there. I don't know what your father has been teaching you, but I'll get to the bottom of it when he gets home........."