Multi-Level Community Forums

We're looking to start aggressively building the community forum section of our site, but I feel we're a little bit limited in what can be accomplished off the bat. I'd love a way to add another level on the forums - for example, our Knowledge Base articles follow this format:

* Category
  * Topic
    * Article

while our communities are:

* Topic
  * Article

any way to add another level to this would allow us to split up our forum in a much neater manner - I believe I saw mention of it in Help Desk 1.0, but not in 2.0.