He needs to ship himself as freight.
Airlines need to stipulate that a coach ticket buys you a seat however many inches wide. 14?, 16? Whatever. If the passenger needs 28, 42, 56, they buy that many seats. I am no friend of the airlines, but there is no human civil right to be jinormous. Fat is a choice. Live with the choice.
Or just check himself in as oversized luggage…. The cargo hold is vast….