AJAX changes the CPM (cost-per-1000-impression) advertising model, so you'll need a different type of ad network. The more mainstream ad networks haven't really addressed the issue for smaller sites, despite the fact that AJAX's popularity is peaking.

There's something called CPI (cost-per-influence) advertising, which isn't based on pageviews. Only one network comes to mind (Coudal's "The Deck": http://coudal.com/deck/) but maybe some Googling may lead you to some others. The Deck will pay you with a predetermined sum that is not pageview based.

It seems like it might be an opportunity for one of us here. Definitely and interesting project idea.