I do think the op's use of "borderline" is problematic, though, as his needs as described fit squarely within what you would expect with that diagnosis.
Not really. Not OP either. But I have a child whose social skills aren't great and who has some attention issues -- without any other hallmark traits of an ASD or ADHD. I'd actually love a Dx sometimes so he could get free services on the taxpayer dime, but alas, he does not meet the criteria.
So when OP says her son has borderline attention issues and some difficulty with social pragmatics, let's accept her word about the severity of his symptoms. Maybe he really is at the margins.
OP: check out Diener school