Do you offer the course multiple times with groups of students, so you need a fresh topic each semester (for lack of a better word). If that’s the case, you could use a theme component (or user training) to encourage people to use the reply-as-linked topic when commenting on the lesson in a particular category each semester. People could then watch the semester.
Another would be to make a fresh category each semester that linked to the content and people could reply to the pointer to the content.
Another would be to use tags for each lesson, then people could watch the tag, regardless of what category it was in, so your theme component would have a reply-as-linked-topic button that also pre-populated the tag field. I think this might be the best solution. I don’t know how to make such a button offhand. I think it would take me an hour or two and would take some people here 15-60 minutes.