Already got as Modman on the way - I liked the idea of the fill tube because without the cap yu can plug it with a breather, so it serves two purposes.
Why not get a set of the old style breathers, the kind that the drag racers used? I would love to have a set on mine, but damn they are expensive.
If you wanted it to look nicer you could have it made from a thick wall aluminum pipe. Thread the inside on one end and turn the other side down and thread the outside.