I can think of a few simple tricks already. One: Host from the main facebook.com domain, either inserting it in the basic html page response from the server, or from an API / content location that cannot be predicted. (ad calls should be indistinguishable from 'normal' content calls). Two, do the same with content locations, so no 'div id="ad"' or anything like that. Should be easy enough.

The efforts I've seen so far from other websites include randomized IDs and class names, and base64 encoded images inlined so the file path/hostname can't be used as a parameter for blocking.

Me too. This is clearly a cat vs mouse game or more like a lion vs mouse and that's what makes it interesting to me.