You should be able to specify a layer offset, changeable at run-time! I should think adding this would be pretty easy, but it would give total control over how each layer is rendered. if you wanted to move a layer, not in conjunction with the camera, you would just change offset values (x,y). When construct 2 renders the layer, it simply adds these offset values to the draw call.
Some kids in a class I run thought this should be a feature, and I think that it is a good idea!
What do people think? I can think of uses for independent layer movement that is not tied to the camera. Sure you, can do it already bu moving each object in the layer, but that can get tedious (even when using families).