Top down light map as a environment map for the main character/Player?

Can a topdown lightmap of a level generated in a 3d modelling application be applied as an environment map to a player character inside of Unity3D as the character moves around the same level? Unity's environment maps are cubic(require four textures). How do we do it with one texture?The Apple team did this via OpenGL ES for Quest that was showcased @ wwdc 2010. This eliminated the need for dynamic lighting & resulted in great frame rates.