Making a main site, then building lots of little sites partially related to it. Build up these little sites with backlinks like you would any other site, then 401 it to your main site. I think this would work if you've exhausted all your link exchange avenues. For example the main site is about car news, you make a little site about car videos or van news. They are still related.
Perhaps a better way would be to make specific pages directly related to the mini site that was reidircted, so instead of doing it to the main page of the main site, you make a page.