Tim,
Luckily for me, there is a 6 inch access port in the floor of the compartment under the helm. I was able to lay on my stomach (feet toward bow, head towards stern) with my left arm in that hole, while my right arm was pushing the hose 1/4 inch at a time, my left arm would pull 1/4 at a time. It was slow, but it was the only way I could figure out how to do it. Without that second access panel removed in the picture, I don't see any way I could have done this without cutting in deck plates. As was said before, that fill line is "clamped" in a two spots in there and there was almost no play in the line whatsoever.
A second set of hands would have really sped this project up for me.