Fake Directional Lighting

Here's what I want to do!

So basically, I just want each direction to be lit a different color based on what direction the wall is facing. Right now I'm doing this with six directional lights - which, as you can imagine, is extremely expensive. Here are the two ways I've thought up to possibly fix this:

1. Write a shader that someone takes a face's vector into account

2. In Maya, assign materials to each face, and then figure out the rest in Unity.

This seems... extremey difficult for what seems, to me, like a pretty simple problem to fix. Does anyone have any solutions for this?