Here's an update: we managed to successfully do an immediate turn, and book all one ticket (Canada --> ICN (wait two hours) --> Canada).

However a cautionary note: the only reason we were able to do it is we had documents from the Canadian government approving the immediate turn from their perspective that the airline was willing to accept so that they could blame the Canadian government if something went wrong. The check in agent was otherwise unwilling to allow the itinerary, and it had to go up several management levels for it to be approved. It was a long day, but it was successful. Just needed a lot of documentation and advance planning.