How about just banning mobile ice cream trucks for fat people? Like the height rulers at amusement parks, we could have scales which could sit on the street. The customer would step on the scale and if their weight is below the "obese" level, then the glass would slide open and they could order ice cream. If they are too damn fat, they would have to move along.
We have a device to do that already!
It is called a "door". If you can't fit through it, you can't get to the truck until you slim down.
"Fatty, fatty; two by four! Couldn't fit through the kitchen door!"
Without enablers, it is a self-solving problem.