PerInstanceRandom?, or how do you do random materials in UDK

[Mist]

So I want to have varying levels of light (emissive) coming from my windows in my UDK scene.

Without having to make loads of materials, what would be the best way of doing this?

I've had a look at the node PerInstanceRandom, but I can't seem to get it working, and all the forums I've looked at, can't get it working either. I'm wondering if anyone here has had more luck with it?

Failing that, does anyone know of another way to get a random value from the material editor in UDK?

Thanks