Its actually a new feature that appears in 4.6.
its still sort of a work in progress, but its getting there.
“Turn this on using the new “Use Emissive For Static Lighting” option on shadow-casting components with Mobility set to “Static”. When enabled, Lightmass generates baked direct lighting from emissive texture sources.
Note: this is a fast but limited version of emissive lighting. Only direct lighting is computed but build time is not affected. It is best used in scenes that have other light sources.”
some information on 4.6: Unreal Engine 4.6 Released! - Announcements - Unreal Engine Forums!