X-rays only through certain objects?

Let’s say I have a white cube, a green emission plane as a “window”, and a red emission cube inside the other cube.
Here is my example.

http://pasteall.org/blend/index.php?id=52061

If I want to keep both emission shaders, is there a way I make the red cube much more visible? At first I thought I could use it as an x-ray but then that would make the red cube visible through the white cube as well.