DepthMasking different objects

I have read and explored DepthMasking as a way to mask an object behind an invisible wall. However, I need to have two different planes hide two different objects. What I am trying to do is have one wall hide a green floor, while the other wall hides a red floor.

The setup is like this:

The green and red floors exist in the same space. The masked area is actually comprised of two separate planes, each taking half of the width.

Eventually, I would like a large number of these sorts of systems to exist at the same time, so having a different shader for each object is somewhat unrealistic.