i cant believe im the only wakeboarder/wakeskater here. If your going to do this, u should probably just buy/build a winch. They use them in wakeboarding all the time to ride in spots where a boat cant fit and hit rails and stuff. Its basically a small motor that winds up 500-1000 feet of rope on a spool and pulls you forward at up to 20 ish mph. They can pull a boarder out of hte water so im sure they could pull you right up hill.
www.hypoxicfilms.com
www.piratewinch.com
check out those sites or go on wakeboarder.com and do a search for homemade winches