Ah, I get what you mean now.
The problem is that when a player types "?hop", it automatically goes to all other players in the session, including FSHost. There's no way I can stop it, because it's not a message that's being created by FSHost.
However, if the player is using FSHostClient (with FSX or Prepar3d), they can use the FSHostClient chat window to click the name of the FSHost server, and then the ?hop message they send to FSHost will be a private message, and nobody else will see it.
The problem, of course, is that not everyone's using FSHostClient (for example, if they're in FS2002 or FS2004), and even if they are, they may prefer to use the chat window built into FS. Or they may just not know they can send a private message using FSHostClient.
Sorry I don't have a better solution.
Russell