Basically, I would like to have a cross billboard (such as the one below) have it's lighting come from above it. In other words, I would like the lighting to be as if the sunshine was hitting it from above.
The intention is for the billboard - Which will have a grass texture on it - To take lighting from the same direction as the terrain underneath.
The best way to do this, I believe, would appear to be with a normal map, making all 4 faces take lighting from 90 degrees upward.
Would this be possible to do with Blender?