The ONLY way I can see getting his attention at this point is hitting him where it hurts. Advertising. Contact Project Wonderful or whoever is running the ads on his site now. Contact fellow web comics, especially ones that advertise on this site. Demand they tell Greg & Liz they're pulling they're ads (and money) until this is resolved.
If any posts crop up about a "Real Life get together" this year, Greg should be hammered for even thinking of spending money on such a thing. Not that anyone should think of attending at this point, we're all so infuriated at him over these developments.
So yeah, I think that's the only way of getting this resolved, unless the e-mail route (email@example.com
I believe) seems to be working?
Edit: Looks like Google ad services (dunno if they'll care or not) and Project Wonderful are the two big advertisers on the main page.
I think this goes without saying, but if we do contact them, it can't be slanderous. It has to be civil, and not "OMG HE'S A &#&@&@ THIEF!", otherwise they won't take us seriously and nothing will get done on their end.