Add info box inside a category?

I'm making a private, members-only area on my phpBB3 board, and I want a category with two forums, which is easy enough.

But I want to have an info box inside that's only visible to people who click on it. I don't mind setting it up so I've got a forum with two sub-forums, but I want the info at the top, not under the sub-forums.

If I set it up as a forum with two sub-forums and put the info as a post, it ends up under the links to the sub-forums, which isn't want I want.

Is there any way of doing that?