The top of the pipe is just pipe...with a cap on it. So, I use a scooper and very gingerly scoop the feed into the top of the pipe.
Another way to do it, which I'd like to try, is to put a Y near the top so I have an angled aspect to put the feed into. a large funnel might be of use, too.
The good thing is that it holds a LOT of feed, so it doesn't have to be filled very often at all.
Check the top video at 0:07-0:09, you can see the cap at the top. If you click this link it will take you right to the 7 second mark
To expound on the Y idea, I was also thinking about making the off shoot of the Y go through the chicken wire so that I didn't even have to go inside the run to fill it, or to grab it to fill outside of the coop.