Well it turned out to be a case of Lars forgetting that airplanes were fun to go on, because on our return flight over the weekend, he was much better.
Aside from a little restlessness at the end of the flight, he did great, which made me feel a lot less guilty for putting him through it in the first place.
He will be taking a few more plane rides over the coming months as we travel to various out of country competitions, so it is comforting to know that he will handle them better.