See this thread Byron and have a look at the clip 3lbgrayling posted on there, it shows very clearly how to do it. You need to get yourself a cheap matarelli lookalike whip finish tool like the one in the clip. When I first started on a WF tool I couldn't do it for monkeys nuts because I'd been useing the wrong kind of WF tool, I picked up a matarelli lookalike (revolving kind) off ebay and just practiced on a big old fishing hook in the vice, literally hour after hour copying exactly what that guy was doing in the clip and I got it in the end and have never lost it since or looked back. I used to always tie a double half hitch by hand and used to swear by it, not any more.
which whip finishing tool?