Great idea! What happens when they get bigger and don't fit on the dashboard anymore? I suppose you could move them to the seat. Also, watch out for those random hot spring days - you gotta open a window or your babies will be toast!
Once the plants are large enough, I will repot and they will be hardy enough to put in the back yard on days that are above 45 degrees and sunny. That should start next week. then at night I will bring them in.