K.B.
I would suggest on having them take a back route if you tie cans to the back bummer, it is VERY dangerous and more then likely illegal to be trailing cans behind a car on the freeway. Some one might call it in to the police or one might be sitting around and who wants to deal with tickets on their wedding day.
Another option is that after they drive away from church they do a quick stop before getting on the highway and take of the cans.