I'm working on a VFX shot where I have created a clean plate that is motion tracked to go over a store sign. I made some 3D text to put in its place, but because the clean plate is shadeless, the text does not cast a shadow on the clean plate. Is there a way to keep the material/texture shadeless and therefore seamless with the original video, and allow it to receive shadows?
I don't know if there is a way to do exactly what you're talking about, but I have another idea.
I would duplicate the clean plate and move it ever so lightly closer to the camera (as little as possible). Then change its material to a transparent shadow-catcher. That way, you can see the plate through/behind it, but the letters can still cast shadows on it.
I'd love to see how well it works ;-)
I hope that helps!