When you get to the zip line there will be a wall of hooks. Take one down and flip it. I did this by laying it on the ground. Now pick it up and grab another hook in your other hand. You should have 2 hooks now, one in each hand, both pointed the same way. Now approach the zipline and hook them both to the line before going down. Once you reach the bottom the achievement should pop. Some people say that it takes a few seconds to a minute or so after landing so don't panic if it doesn't pop right away. In my video, I land and the video stops but I actually turned around and walked back to the zipline and reached up to grap the hooks again before the achievement popped. You do not have to hold onto the hooks until it pops, just hold on all the way to the bottom.
https://vimeo.com/736335723