This article notes how a quick thinking motorist saved himself from being towed for having an unregistered car on the road. He called a friend on his cell phone and his friend registered him online. Since the registration took effect immediately, the tow truck was canceled.
But there's no real reason for the tow truck to be routinely called. Why not just upgrade the policeman's electronics to do the registration? The service charge could be rolled into the ticket and the whole thing run on the driver's credit card.
Let's see, that would save a day lost to getting your car back, keep more money for the city and reduce the amount of cars damaged due to towing. It would be more efficient and everybody could get on with their lives a little sooner.