I think that this whole idea would work better if tippers got credit for their tips. People like to patronize good writers, but they want to get credit for doing so.
This is what we are trying to acheve with youtipit (
http://www.youtipit.org). We are looking to create a community around tipping and find ways to reward people who tip (score, badges,content, promotion etc) If you have ideas on this let me know....