Odd render strategy for cartoon mouth?

I saw an interesting way of modelling and rendering a cartoon mouth, and it looks super useful. Here’s the original:

How would I do that in Blender? Preferably, a way that would work with a normal toon shader or ramp shader.

To get the full range of motion in the head and stuff, you’ll want to render the mouth in a separate render layer, then put it on top of the rest of the head in compositing. Looks great! It gets the hand-drawn effect much more accurately like that.

The idea is not altogether new …

“Holy Clutch Cargo, Batman!”

(See especially the section on “Technique.”)