“a crossing of the English Channel which, for the first time, will require a refuelling in mid-flight.”
Why not bolt on an external fuel tank, that he could use for a seat? A modular add-on option for extended range/longer duration. Just be sure it has internal baffles, to reduce sloshing around from effecting balance.
“Why not bolt on an external fuel tank, that he could use for a seat?”
Too much weight, probably.