As I wrote above, tow-charging is theoretically possible, but it's way too dangerous for most people. If you happen to do it without braking and at constant speed, that's fine. But the real world throws all kinds of crazy drivers at you.
Here's an experiment I often do; try to go place without using the brakes at > 5 MPH. In theory, this is possible. In practice, there's almost always some idiot cutting me off even when going at constant speed that force me to use the brakes. If I had a 3000 lb car behind me in a tow strap, guy in that car better have adaptive cruise control quick reflexes or very very long tow line which may not be legal.
Tow bar would work, but I think SparkEV is prohibited from using it. There was discussion about this some time ago.