Is it possible to render an alpha/matte channel?

I’m in the process of evaluating different game engines for a broadcast graphics project that I am working on. It looks like Unity is capable of everything that I am looking to do with the possible exception of this one. I can program so doing a custom script or plugin isn’t a problem.

What I would essentially like to do is end up with what you see on the screen as a color image and then also have a black and white image that represents the alpha channel. For example, if something is present, it will be pure white, and if nothing is present, it would be pure black. As a side goal, it would be great to be able to force the alpha channel to be one way or the other based on some geometry that might not appear in the color image.

If I were to buy the pro version would I have enough access that I could pull something like that off?

Yes, this is possible.

Thanks!