Snatch Block and tackle, 300-500 feet of rope. Tie the snatchblock off to a tree, hook up rope to down sled and tie off to a running sled. Running sled goes downhill while towing sled up hill. Make sure downhill rider gets stopped before a knot goes thru the snatch block, makes for a very impressive rider launch if he doesn't get a STOP signal.
Wire tie small trees in place of the track. Tobaggons??
Or, two sleds tow down sled out. Many ways to skin this cat. Requires lotsa beverage, steak and lobster, and new belts for the towing sleds.
Or just call Gravy for the Heli, it keeps friends