Just shot this earlier today at Hummingbird trail in Simi Valley. Since there are no trees at this trail, I recruited two really cool people to help me set up some shots for my "Uni-Cable-Cam". (about a 1:30 in)
We rigged it so that each person could hold one end of the line very solidly, and it worked out surprisingly good. They even let me hook up their GoPro HD for a few shots...I MUST get one of those. The HD quality is amazing and cyrstal clear.
Hope you enjoy and drop a comment if the mood strikes you.