Light mapping without shadeless?

How does one implement light mapping and also have the ability for dynamic lights to light the scene in the blender game engine? If you bake a texture of a scene and make it shadeless, then realtime lights in the scene will no longer effect the materials. Are emission maps the answer?

And if there is an answer how much will it hurt performance? Thanks for any replies.

I did not think emission maps used any more then a diffuse map, I am unsure though.

Anytime I make an object emissive it definitely hurts my performance, so it’s not necessarily about the texture. And I was also wondering about any solutions that I don’t know of that might impact frame rates.