So I was looking into custom lighting, and after looking at this thread,
http://www.polycount.com/forum/showthread.php?t=78408
I dug in and tried to replicate what Sprunghunt was doing. And with a little more fiddling managed to get it working in color by splitting the RGB and recombining it in faux-CMYK. I added a depth based scale to the halftone screen too. I'm going to keep working on it and posting here and see if I can't get something like it working as a post process effect.
You can also see where it obviously needs more work.