Can't be done. I've given two indisputable proofs which, even if they don't indicate a spherical earth, at least DISPROVE the flat earth model. Neither of them are addressed in the FAQ (I've looked).
1. The position of the southern cross. I invite any GENUINE Flat Earthers to come to the Southern hemisphere (they all live in the Northern Hemisphere, funnily enough), and explain how the southern cross hangs over the south pole no matter where you are - this is impossible in a FE model.
2. I've been to Antarctica. Thousands of people have. And if it were just an "ice wall" we were visiting, I dare a FE'er to explain how we experienced continuous daylight (or continuous nighttime, depending on when you go). Also impossible in a FE model.