Comment permission only to author and/experts

I'm trying to have a question/answers page, wherein authenticated users can ask a question, experts will answer and later only the author of the question or the expert, should be able to add comments. So its like a discussion between the asker and the expert while other users will only be able to read the q/a page, but may not comment on any question which is not posted by them.

Is this possible with faq_ask? Or is there a workaround for this?

Help greatly appreciated! :)