And in H.S. teachers can be reluctant because they are so worried about cheating. In this case I think it's fairly easy to let DS to the main part of the test (multiple choice) with the class. The teacher could give him a version without the last 20% (the short answer).
The school has set times twice a week for a student to makeup a test or get help from teachers. This is when students make-up if they are sick. He can then come in then and finish the test when kids who were sick would be making it up and the teacher could give him a reasonable amount of time just for that part. It would be fairly easy and not be too conspicuous.
