Two camera rendering for selective glow

Hello,

I have a game that involves cubes of different kinds. One of them is a crystal cube that changes colour based on the colour of a cube that is clicked on. Everything else is working, except that I can't get the crystal cubes to glow. I'm using Unity pro.

I found this shader: http://forum.unity3d.com/threads/13107-Glow-effect-with-adjustable-threshold-%28enjoy%29 which is great and gives me the EXACT effect that I want. However, I only want the glow on the crystal cubes. That's not what's happening.

I've seen questions similar to this, and a lot of the time, when using the stock glow shaders, they suggest setting the alpha on non-glowing objects to 0. This won't work for my purposes.

I've come up with a potential solution, but my experience with multiple cameras and the way that rendering works is limiting me.

The shader I mentioned comes with a script that attaches to a camera and makes all of the objects it sees glow.

My solution is:

Use two cameras, one to render everything but the crystal cubes, and one to just render the crystal cubes. On the camera that renders the crystal cubes, use the script that came with the glow shader.

I've been able to create a new layer for my crystal cubes, and set the crystal camera to only render that layer, and disabled rendering of the crystal cubes in the original camera. But I can't get the cameras to render together. I've tried changing the depth on the cameras, but that doesn't work.

Additionally, I'm using the Particles/Additive(Soft) shader for my crystal cube because it's the only one that looks right, but this won't allow them to glow.

I appreciate any help.