overlay input from more then one camera

Hey guys,

I am trying to make an application in which there are several layers which never interact with each other, so I was thinking that if I could overlay the input of several cameras that would be a clean workflow.
A common example would be making an interface overlay or in my case adding background and foreground elements that always stick to the camera.
Is this possible as of yet?

Can you please show an exapmle, if there are any? Or specify a bit more what you're trying to achieve

Hey sorry I can't provide the full scene but here it is what I am doing. Hope it makes sense.
Basically I have two planes - background and foreground - resized to fit in the frustum of the camera to create the feeling of an environment. In between I have 3d models.
It works but it's kinda hacky. Let me know if you guys have better ideas :)
You can see the setup on the left and the camera view on the right.

several layers which never interact with each other

What do you mean as interact? What kind of interacting you talking about? Physics, shadow casting or something else?
If you plan to imitate something like in blender internal layer composing, so the leyers like there is not supported. It's difficult to understand what you want without example.Сan you write step by step what you want to achieve?

Thanks for taking the time to reply and sorry I couldn't make it clear right away.
I'll give more in depth description when I get back to work next week.
Thanks again guys!