If you wanted to keep it all in bryce, you could take a "square" flat 2d face object, track it to the camera, and position it so that it's right in front of the camera. Then apply a bunch of materials with heavy transperency to the face, and animate the scene as usual. It's like using a gel, or a filter, only in Bryce. Only problem is it might take a lot of work to reproduce the effects you are seeking within the Materials Lab... Good luck!