Love Andrew Price. Very clear. Thanks for posting!
Yeah, this was a very different way of approaching it than I had ever thought of. In an old render, I was trying to put snow on an abandoned/destroyed AT-AT Walker. I used an empty and UV projection and it was way more sloppy and unrealistic than this... while being extra work :P
Ye it's nice when you come across an elegant solution for something like this. Seems like you have to have a good problem solving mind when it comes to the node editor.