The way to prevent rolling is to hold down a brake lever

You’ve reminded me that I need to do something similar but for my e-scooter. When folded up, it will try to roll away as the bus yaws or pitches. But my plan is to drill a hole through the bottom of brake lever housing, so I can push a bolt up that will jam the brake lever whilst engaged. And since the bolt is facing downward, it should fall out when I squeeze the brake, quickly putting the scooter back into action.