Just go to a plumbing store that sells black or galvanized pipe fittings, and find either a cap / coupler or a pipe nipple large enough to go around the seal lip.
You got any large sockets?
How about some hole saws? Take a 2 x 4 preferably hardwood, and cut a hole so the lip will clear, then stack a second 2x on top and beat on that.
I was lucky. I've got a bunch of "special tools" I got in a deal, and some tool I know not what had the perfect size hole