You may want to try a vacuum cleaner... There's a video with Oscar showing it on an epic surfski floating around. You tape the vacuum cleaner to the hole at the rudder end and then feed the dyneema in at the front slot. Without vac I couldn't get the dyneema pushed in more than about half way on my nelo 550. With the vac it was child's play once I got the vac hose reasonably well sealed around the opening. I think in the video Oscar feeds it in the other direction but I had the adjustment blocks already attached, so I had to go front-to-back.