It sounds like you’d want to render out multipass files. You basically assign a “compositing tag” to each of your objects and give them each a different buffer number in the “Object Buffer” tab. Then in your render settings under “multipass” you will click the “Channels” arrow and click on “Object buffer”, referencing as many objects as you have assigned with different buffer numbers. Then set up the way you want them rendered out (Quicktime, bitmap sequence, etc).
I use this for heavy scenes to control the color, brightness and contrast of each object. It will render out an alpha channel for each object to which you have assigned a buffer. You could also use these alpha mattes to “mask out” other things in your scenes as well – hopefully, this is what you’re looking for.
Best,
Brian