Dont think that hasnt been considered. I am still working on how to power a rope tow off the PTO on the tractor.
As soon as I saw the tractor at the bottom of the "ski run" I thought, you have the tractor so there is the rope tow, almost ready to go.
So, don't bother with the pto. Instead take the tire off a rear wheel but leave the wheel in place, then sling the rope down to a set up second wheel mounted horizontally on an axle, firmly secured in the ground. Or the second wheel can be mounted vertically on a more complicated set up.