Have you ever tried this? Do you have an account of someone who has tried this?
Considering it's never been done, the belief that it's possible is entirely reliant upon the assumption that Earth is round. Take that assumption away and you have an unfounded assertion, and certainly nothing that would prove the sphericity of Earth.
But feel free to try it. Just make sure to bring along magma-resistant clothing, because if what you're trying to prove is correct, you'll need it.
--Chal