While I applaud the sentiment $20 per hour is too little to make me care and enough to make me start thinking about money.
A much better way to deal with this would be pushing laws to allow for tax offsets for contributing time to charities (open source ones). Seeing $10 per hour (after tax) that doesn't inspire me much.
Being able to write off my full time wage as a tax deductible would make me vastly more motivated to document what I've been working on and work on a lot more of it.