I don’t have school recommendations but if he really struggles with writing to that degree, he could seek out humanities or social science courses that are more exam-based than writing based. Also, at some schools, it might be possible to knock out writing requirements with courses in technical or non-fiction writing that would also serve him well for CS.
I also would not underestimate the services and accommodations now available at colleges and universities for students with learning or cognitive disabilities. I would ask about this as your son moves forward.