Two more ideas:
If you don't know many people in this sample, you could just buy traffic to these articles (from that target audience -- facebook or google would work great, stumbleupon should also do), and then judge by the total amount of time spent reading by 100 visitors.
Or hang up the articles as flyers at your local college campus (though this assumes that audience), and see if anyone picks them up to read them (and how long they read if they do).
Several people have written articles on efficient charity -- throwawayaccount_1 has an excellent article hidden away in a comment, as does waitingforgodel. Multifoliaterose promises to write an article "at some point soon" ..., and louie has actually submitted an article to the main LW page.
What I'd like is for throwawayaccount_1, waitingforgodel and multifoliaterose to submit to the main LW articles page. People will read the articles, and hopefully vote more for better articles. Srticles not submitted to the main LW articles page are not eligible for the prize.
Note that it is hard for me to judge which article(s) will actually have the best effect in terms of causing people to make better decisions, so at least some empiricism is desirable. Yes, it isn't perfect, but if anyone has a better suggestion, I am all ears.