Jim, of course there is a way to enlarge the opening without sacrificing structural integrity...just make it bigger! Seriously, the splashwell flat where the pie is currently located is not a "structural" part of the boat, in that it not a load bearing part of the deck. So enlarging the opening to install a hatch is no problem.
I really wish the engineers at AS could have foreseen the difficulties accessing that fishbox pump 10 to 15 years ago, they would have never specified locating it where it is... :x