Try to do it in post! Like: DFusion, AEffects....... And you'll end up having a lot more control over it!
You can also try to animate a non visible plane (or cube)to reveal the object and set it up, so it'll add itself to the alpha of the obj. This way you'll see the whole object while viewing the color channels, but if you throw it together in a post software it'll use the alpha and it'll hide the rest of the object for you!
Makes sense?
:::::vik3d:::::