Edit: Oh.. you clearly said "in-game" and I failed to read it. Well... here's an out-of-game one if you're interested....
Browse For Speed has some admin functionality - you get all the txt going on in the server (chats, pitting, penalties etc) and can send msgs, and has quick ways to kick/ban/force spectate people. It does it via insim, and should work with the relay as well.
When I use the "Administrate..." option from the right-click menu of my server, it brings up the window and when I connect, it doesn't show the users on the right hand side. It only shows msgs. The msgs don't contain users either, just <>.