Cell/Toon Shading with Forward Renderer?

I’m wanting to implement Cell/Toon shading in the project I’m working on, which I’d like to take advantage of Forward rendering for. There are dozens of resources on making a cell shader using Deferred rendering, but with Forward rendering I can’t access the GBuffer to use the core nodes those shaders need.
I’ve been looking all over the place, but can’t find anything on doing Cell shading with the Forward Renderer, other than this ( Where the guy making Lucen mentions the Toon Shading model in the custom build of Unreal he’s using.

Any pointers on how to do it, or at least what questions I should be asking? I’m still new to Unreal, so I don’t know all the ins and outs of the engine/renderer.

Found this blog in Japanese and put a basic shader together (Thanks to Google Translate…9/12/01/000735 ), but it’s only two-tone, and relies on the directional light saving info to a material parameter collection. I found a workaround that doesn’t require that though.

It’s a start.