Perhaps positive G could be simulated if a simulator is mounted in a CENTRIFUGE... But negative G would still need another idea, I suspect.
RVSM may be, or is, an ATCC requirement. This could be relaxed for a finite time, say 15 or 20 minutes, by the current controller to allow a small amount of practice at hand flying when Traffic allows.
Someone mentioned a year or two ago that he had had to hand fly a B707 at F/L 41.0. He said that the two pilots found that they had to take it in turns for 20 minutes each.
( They would have covered much the same Air Mileage as I did, hand flying a York for several alternate hours on long sectors, also without A/P.)
LT