1. bid on high traffic, low cost keywords.
2. Use landing pages with content geared towards attracting High paying adverts
For example, you bid on "free stuff", pay 5c a click. Then send people to a page about class action lawsuits or something, where adsense is showing them some adverts for lawyers, with a $5 per click...
Similarly though, you'll get penalized for this now, as having a non-relevant landing page, and your bids will go up.
I'm glad they got shut down. Sitting in the middle doing nothing in a loophole isn't a valid business model for long.