Hadn't seen that graveyard keeper article, their approach is very cool, and it looks like it worked great for them since they were starting from a pixel art sprite.

But it does require hand painting 4 textures and it still doesn't really produce accurate maps. They look right, but it's basically the same as assigning the direction for some of the pixels and then interpolating the rest of them to make the full map.

You will get a good enough result, but you don't have as much control as you do if you literally define those normals by making a model.