Basically he sets up microsites that look well designed (it's usually a very simple single page design) and have relatively funny content aimed at the Digg community.
He then submits that content to Digg, pushes it, waits for it to frontpage and then changes the page to have a "sponsored by" or similar message at the footer or header, but so it looks like it's part of the actual original design.
He does this often (perhaps twice a month?) and the cost is very minimal to him, but sends several 10's of thousands of users to his main site and each of these microsites provides Google juice for his main site.
He has also managed to pickup additional traffic from bloggers looking for content via Digg.
Since your main target is teen-20something females, I'd probably start thinking up comedic microsites related to various celebrities? They always seem to be a fairly easy to hit target.