Yes, it is time-consuming. No, there isn't any automatic way to do it.
Thanks for the reply! I feel better knowing that it's just the way it is, not that I'm missing something because of my lack of knowledge in AE. Thanks!
Yup -- people who make faux 3D out of stills run into this all the time. Actually, I'd think the Photoshop work would be tougher.
I think what you want is to adjust the scale of a layer as the distance from the camera changes so that the layer remains the same size. This is useful for the kid stays in the picture effect. If that's what you want try adding this expression to the scale value of a 3D layer. Make sure that auto orient is switched to towards camera and you should get what you want:
C = thisComp.activeCamera;
CP = fromWorld(C.toWorld([0,0,0]));
L = thisLayer;
LP = fromWorld(L.toWorld(anchorPoint));
d = length(CP, LP);
z = C.zoom;
r = d/z;
r * value
This will keep a layer the same size in the composition no matter what distance it is from the camera. Let me know if that solves your problem. If it doesn't I have a bunch of other expressions that will help with the 2.5D or Projection Mapping or "Kid stays in the picture" style of animation.