The original rope ski tows were not much different. They took a tire off a model T, and jacked up the wheel, and put a bare rim back on.
Rope looped up the hill to a front axle and rim at the top.
The tow runs at all times, so when one rider grabbed the moving rope, the load was not so heavy as to stall it.
No reason it wouldn't work, but you might need to make a custom deep dish rim for the rope pully on the hubmotor so you don't jog the rope out of the slot. Might be perfect with a cast rim scooter hubmotor, jacked up to 2000w, with some plates bolted to the rim to make the pulley have a deep slot.
I don't think just flipping a bike would work well. You will need a pretty secure, non wobbly way to attach the motor. Something like a modified bike frame designed to strap to a tree trunk perhaps? Something that hangs from the car's tow hitch? The top pulley can just be a big pulley attached to a tree.