@coffeegal Submit the other score. “Strongly encouraged” means “we don’t require it, but we expect you to have a good reason why if you couldn’t submit what we request.”
“I didn’t think that score was good enough to help my application” is not a reason why you couldn’t submit it.
If a choice comes down to either your son or a similar applicant who submitted the scores they requested, they would be reasonable to admit the applicant who followed their instructions.
In other words, they would likely frown more on his application lacking the available score, than they would on a 680 being “too low.”