Here’s an idea: Right before Linus gives his scriptural speech, pause the play, stand up and identify the complaining parent by name, have them stand up, and then announce that the next portion of the play will likely be offensive to them, and that they can leave the auditorium for a few minutes. While they leave, stand silently and watch them to make sure they’re out of earshot, and then commence with the play.
Why don’t they substitute the video of the Apollo 8 astronauts reading from Genesis on Christmas Eve.