I love hearing stories like this

Thank you for sharing such a positive story

If you have his email address, you could send him a note (or call him of you don't). I am sure he would appreciate the feedback. As a substitute, we don't often get a lot of feedback. Also, you could help him by letting your principal know what a great job he did/letting other teachers know about him. If you do decide to recommend him to other teachers or let the principal know about him, I'm sure he would like to know that as well
Hope this was helpful!!