Hi Domonkos.
This is not a method of doing what you asked, but it is an alternate procedure which might be worth considering.
I usually create a hidden forum ("Staff") for these discussions, with Ratings enabled, and showing the Average rating as the aggregate. Ratings can use a custom scale (e.g. Hide, Publish).
Staff read the students' posts in the visible forum ("Students") which has no Ratings, and staff usually respond publicly in there.
However, staff can select an exceptional thread and Move it to the Staff forum. (This button is usually at the top right corner of the forum.) There they can discuss it, using the Reply button, out of view of students.
Staff can vote on publication by setting a Rating (at the bottom left corner of a post). If a particular reply should be public, staff can Split the thread (an option near the Reply button at the bottom right corner of each post) and Move the fragment to the Students forum, where students can find it, but cannot see the rating or the discussion above the level of the Split.
This approach deals with flaming, trolling, copyright and privacy issues well.
Of course, staff should subscribe to the Staff forum so they don't overlook hot issues.