Hey Chillybody -
I am looking into whether this exporting is possible but I can point you to where they are located in the engine. After you build lighting, go to World Settings>> Lightmass >> Lightmass Settings >> Drop Down for additional options >> Lightmaps. You can open and view all of these textures and add composite textures with them, but currently there is no export option.
I will keep you informed -
Thank You
Eric Ketchum