The United 232 DC10 that landed using differential thrust would have been flown as they did whether or not the check airman in back had come up to the cockpit or not. They had no choice and the only solution to get it on the ground under control was using that technique.
For some reason the captain elected to let the pilot sitting in the jumpseat operate the throttles to line up with the runway. All went well until the power was reduced for touchdown and it cartwheeled off into the corn field. A lot of people survived so the teqhnique worked but the captain might have had a better perspective from his normal flying position making the final adjustments from his seat in my opinion.