Codeigniter's built-in page cacher

[eluser]Unknown[/eluser]
So, it's pretty cool, but... I wanna show cached pages to un-registered people such as spiders, and people who don't need registration.

When I use $this->output->cache(5) CI creates cache and shows it to every user. It makes problems because I have a toolbar for registered users, also this feature prevents correct log-in procedure.

How can I make CI to show cached pages only for clients who doesn't have

Code:

$this->session->userdata('log_in')

variable set, and generate pages as usual for clients that logged in?