You have to re-apply the lightmap in code using EntityTexture. It works if your model has the alpha information in it (ie. exported with B3dPipeline or LightBulb). The trick is to take the lightmap off of the alpha surface before export.
EDIT : Scratch that :( It all seems to have changed. That method used to work (1.84) but it seems to be broken now.
EDIT : Scratch that :( It all seems to have changed. That method used to work (1.84) but it seems to be broken now.