Add new category to entire site

[eluser]Dauntless[/eluser]
-subdomains: I can create subdomains for the two parts, but how would I be able to know (in CI) if I'm in sales or rent ? Just explode the url and retrieve it manually ? And wouldn't this mean that the site has to be hosted on both subdomains? (=> Harder to maintain)
-custom routes aren't really what I need...