Indeed. Or use nodraw on a func_brush with shadows disabled. Apply it to that should work. But baring in mind it wont physically be on the model, so you'll need to be accurate in getting the brush to follow the surface of your model. You're limited with what you can do with this though.
Your best bet would probably be just to make your own skin for the model including the overlay on it. I'm sure someone around here could pull that off for you since A) the materials are already there and B) you don't need to edit the model mesh (which is what most time consuming model work involves).