Don't do it. The 3 inch shell will do almost everything you could ever want to do. I shot 5 3.5 inch shells ONE time, and will not do it again. I had a friend with a new mossberg turkey gun that would not cycle correctly. (the knuckle-head didn't read the manual, and failed to apply gun oil where required). I cleaned, lubed and shot that gun, and my whole side hurt for 2 days. This was at the same time I was shooting A LOT of skeet, and a fair amount of rifle ammo.
If you need that large of a shell to hit the geese, step up to a 10 gauge shotgun. Otherwise have fun with a 3 inch chamber and learn your limits.