Yes, I used an external vent. Sorry, I have no pictures of the fix, and the boat is sold. I still had a slight problem if I tried to refill over 3/4 speed on the pump, but nothing like the old way.
I have seen it done 2 ways. one is to cut the hose at a point where you can reach it and cap it. Another is to remove the fill assembly and fill the vent with Permatex or 5200. That involves removing the hot water heater and is a royal PIA. I would recommend a combination of the two. Cut the vent hose, insert a bolt and clamp it. On the other end, inject some Permatex or 5200 and feather it smooth over the vent hole and let it dry. you should be fine.
In retrospect, if you decide to go the first route, Cut a hole in the cockpit wall and insert an inspection port when you are done.
I am convinced a lot of the problem had to do with the way the fill hose is angled as well. I would venture to guess if you were to put a level to it you would find it running uphill in spots, hence the need to fill so slowly. That too is fixable, but not nearly as easy considering the location of the tank.
HTH
Good Luck