"Theming" Mattermost to hide channels

I'm putting together a project which will involve users having discussions with one another -- private, one-to-one discussions, about a particular topic. I could of course write something which allows exchange of messages back and forth, but I thought that it might be actually better to have this handled by something which is already good at this: that is, Mattermost. So, imagine that the site has, say, buyers and sellers; sellers can put up various items for sale, and buyers can buy them. The conversations piece is so a seller and a buyer can have a conversation about an item. It would be implemented as being a private Mattermost room for that (buyer, seller, item) key. But I don't want people to think of it as a room among many other rooms. Is it possible to "theme" Mattermost so that I can include the discussion part in another page, but without showing a list of rooms or anything like that? I could of course write a completely custom in-web-page Mattermost client which only connects to one room, but I'm hoping there's some way to do this that doesn't involve that much work. What am I best to do here?