First let me address your question.
Short Answer - No
Real Answer - No because it is an incredibly dishonest and stupid question that would require the invention of several new realities to even begin to address it.
Expanded Answer -
I will start by admitting i don't really know what you mean by an affirmative claim. That sounds like an insurance term, but if you are referring to Philosophy and the burden of proof, then I am not going to get into a game of onus tennis. For the majority of people it would surely be commonly agreed that you are the one making an extraordinary claim but putting that to one side let us look again at your question.
This claim you keep positing is not a claim made by ANYONE... EVER in the threads or discussions here concerning your theory of a flat earth. This is perhaps the clearest indication of how your belief is only able to be maintained with huge amounts of constant intellectual dishonesty on your part. Much like the idea put forward by you, that only evidence seen with your own eyes is admissible in building a cogent model of history and science. An idea you completely rejected when using fake photographs to try and lend your holocaust denial theories some..i was going to say gravitas.. but let's say weight instead.
Nobody claimed that the oceans ( standing bodies of water) conformed to the exterior of a shape or the globe. Quite the opposite. They fill basins and containers. The question you should be asking is why does the water not fly into space? The majority of people on earth accept the best possible explanation for this we have arrived at as humans and call it Gravity. You have already made it clear you do not believe in gravity and so will need to explain to us why birds do not shoot off into space, why the sun doesn't fall on us, why water flows even? Do you believe water flows ?
Another problem with your pseudo question is the assumption that you can model the earth to scale, complete with all the forces of physics that act upon it. The biggest problem though, and the Elephant in the Room, is the ludicrous idea that we should be able to stand outside of the planet we are on, flat or spherical and conduct this experiment independent of the forces of this planet. The biggest problem though is that you will never believe any practical demonstration anyway unless you witness it first hand.