_{This "sample thread" will be linked to this other one, so that a "backlink" from that one will point to here.}

The suggestion consists mainly into write your message to the user(s), opening a dedicated thread here (or, if you like more, into a "Moderation, comments and OTs" sub-forum), then to insert a short post in the original thread, where you like to do your moderating action, like "Please @user123456, have a look to here", where "here" links to this (moderation) thread.

This way, every next (users') answer, which is usually made at least for respect, won't go into the main thread, as well as further comments from others.
This is, technically, a "fork" where moderation can continue without harming the "main" thread.
Hope it helps in having a more clear dialogue and moderating action, as I think that even you admins/mods, most of the times, write less than you like to, only to avoid cluttering the main thread too much, and to give the moderated user(s) the opportunity to answer without cluttering the main thread by themselves too.

**Mod Edit** moved from Off Topic to Feedback Zahira, 10/072017