Start and maintain a $100/month adwords account, and magically, one's domain gets free SEO (moving up in ancillary search results) --> every S.E.O advice on the internet openly states this.
Someone with deeper pockets and some free time could test this I suppose: Start 6 blogs with mediocre content - the goal being to avoid getting organic links from other websites. Buy $100/mo/site of AdWords for 6 months. And then measure which one performs better in searches.