Usernames as subdomains and a root website

[eluser]whizzer[/eluser]
I guess I'm know explaining myself properly. I am redirecting all my subdomain requests (ex. test.site.com, username1.site.com, user.name.test.site.com) to my root website - site.com. There I have an CI installation. In a hook I validate whehter test, username1, user.name.test are registered users. If not or if site.com is accessed I want to show my main website. However, if there is a registered user "username1" I want to show his blog. Here's how I think it should work:
Controller "site" with method "index" for my main website. It will be set as a default controller, so accessing site.com will show my site.
Controller "blog" for my user's blogs. However here I have a problem. If the user accesses username1.site.com I will know (using my hook) that he is a valid user. But how will I load the contents of the blog without adding class and a method name. Ex: username1.site.com /blog/index will work, since in the blog controller I will know the username (username1) and I will be able to load the contents. But I don't want that /blog/ part of the url.
Any ideas?