if you really want to get away with it. I had a predator 212 trailer that before i broke it and delegated it to the future projects pile under the porch, but before all that I was pulled over once out of 4 encounters seeing cops, thats 25% odds. That was suprising because the law on motorized bikes specifies the engine must be part of the vehicle, yet a trailer is not part of the vehicle, so i think if i was in court, i might have been able to stand a good chance due to the phrasing of the laws. traction equipment (which is kind of what a pusher trailer is) fall under agricultural traction equipment in the state of NJ, and require no license or registration cause I guess poor farmers idk.
What would work would be a predator 212 generator on a trailer or something. Bridge Rectify that 120 AC to 96 V DC (can find a switching supply off aliexpress) and use it to power an ebike.... Skip the battery charging, no need any battery, just power straight from the mains. Will probably lose 30% do to efficiency losses, but the law would then be on your side completely. Its not a bright idea to then have it charge a battery cause that adds further losses, and you cant charge a battery at 1kwh or 2kwh, so your wasting generator power. The state laws on ebike say any ebike of less than 750 watts is exempt from license, registration, etc... The problem is can they prove beyond a resonable doubt that your drawing more than 750 watts? Are they going to take a clamp meter under full load and get current. No! So your safe.