It would actually be the easiest experiment in the world.
Take a 4-inch telescope and and eight inch with two observers and watch a ship sail away from Port Melbourne.
You could literally confirm flat earth theory within the hour. And yet our flat earth boosters here refuse to conduct it- even after we offer them all the equipment to do it.
I guess it's easier to wail away behind a keyboard and quote religious verses like the brainwashed sheep they are.