How can I help cycles to see material index through a mesh?

I’ll try my best to explain my problem. I have these car tail lights. I’ve set light emitter material to MaIndex of #1, cause I would like to create mask for compositing. But the problem is that the emitter is behind the tail light cover panel and cycles won’t see through that.

Is there anyway to get this done without rendering in multiple layers?

Here’s a photo what I want to achieve. This was done by hiding the cover panel, but cant do that in final render.