Alpha issue with windows and scenics

[Streetwise]

I'm having a heck of a time with one particular interior that I'm doing with getting an alpha channel for my window scenics. Even setting the alpha contribution to 0 (or -1) on the scenic plane doesn't do it. Of course I could set the alpha contribution of the glass to 0, but the issue with that is that I loose the building exterior details on the other side of the glass to alpha when I only want the scenic to be alpha. Lastly, I do have a plane light in the window, but it's set for invisible, so I don't think that's the issue. Yes, I could always remove the glass, but I would rather not if possible.

Thanks.

Dave

[Morne]

How about using a multimate instead for the outside plane?
That way you can make your own alpha in post