Load Interface?

[eluser]ee99ee[/eluser]
Hi. I'm using $this->load->library() to load a class library, but how do I load an interface?

I tried:

Code:

$CI =& get_instance();
$CI->load->library('Billing/IBillingSystem');

But apparently that requires a class called IBillingSystem and not just an Interface, which is all that file has.

-Chris