Suggestion: if the instructor can also bring in another knowledgeable person, they can receive real-time email/chat questions, and try to answer them, or aggregate them in a meaningful way so that the instructor can address them.

I don't know how well this suggestion will work in the general case because it requires two people who are capable of teaching the course, but it may help. Particularly if the person fielding real-time questions starts seeing trends.

Also, if you can't do that, maybe you could set up chats with 6 (or so) students each, who could try to answer each other's questions.