Render only scene content — not camera feed

Hey there,

Really enjoying working with Vuforia so far. I haven't been able to find an answer or solution to one thing:

How can I not render the video feed from the camera in my scene? For app-specific reasons, I'd like to acquire and track targets as usual, but to *only* render the 3D content in my scene, on a black background — in other words, hiding (or not drawing / rendering) the video image from the camera being used for tracking.

This seems like a simple thing but I can't work out how to do it. I could draw a large black plane in my Unity scene to obscure it, but I'd rather not draw it in the first place, to save the processor cycles. I'd really appreciate any assistance you can offer.

I'm using Unity 4, but it would be useful to know this info for native apps as well.

Thanks very much!