I'm not sure what you want.... you say you want to combine the dynamic shadow with lightmap? this isnt possible with the current shadow method, because it's just overlayed on top of everything else.
what the engine ought to do is to give you access to a texture rendered from the stencil buffer, which could then be projected onto everything and blended with the lightmap in a single pass... alternatively, this could be blurred a bit for soft shadows.
But since it doesnt you cant :P (unless you make a dll)