maybe try plugging in an hsv node between each texture and the main node and saturating the hell out of it, then rendering toon style, as said earlier, with thin lines.  even the shadows are saturated.  i would add the node to the specular, too.  you gotta break up smooth color and  push the colors off in tangents.

anyone notice how the first beer guy has the beer color reflected on  a forehead wrinkle?
i would try that with a little spotlight.
isn't there some python or something somewhere that will allow us to change the color of the shadows?  that seems to be what's needed here.
 

 

 

go that way really fast.
if something gets in your way
turn