That school should not be in the same league then. The rules were played by, there is no mercy rule, they can’t spot another team 90 points to make it ‘fair’. and they cannot, apparently, stop a game early.
But, on a humane and sportsmanship basis, he could have told the players they had a "3-pass" rule before any shot, or something similar. I've seen that done by coaches in a youth hockey mismatch--the team that's way ahead works on some other facet of the game, and if after that the shot goes in... well OK.
Bull, there’s plenty the coach could have done. He could have let his 4 or 5 play point guard and put his 1 and 2 underneath. He could have required only left handed lay-ups. He could have fed all passes through his weakest player. Any of these things would have honed his players’ skills that will help them later in games. Instead he chose to humiliate a demonstrably weaker opponent.