There are a lot of webcomics that use
Project Wonderful for ads, it might be worthwhile your friend creating some adboxes there. It's free to do, and although it likely won't raise a lot of money, it WILL raise awareness especially if he's prepared to throw a few dollars into advertising on other sites as well.
Although Project Wonderful isn't one of my top 3 referrers it is up there in the top ten, so it does work.
~Autumnflare
