Hey Brian, I've been doing a little thinking on the diffusion thing...

Now, first off, I don't know what you've tried, and secondly, I have no idea if this is even feasible, but what about adding in fine particles of something semi-reflective into the mix? I'm thinking ultra fine glitter...

A company called Mark Enterprises makes some "Ultra Fine" glitter, that is so insanely tiny, it's hard to distinguish individual particles with the naked eye. And, it comes it in many colors, including glow in the dark!

(OK, so the reason I know this, is because I glitter bombed a girl for valentines day last year... Yeah, I'm a nut.)

Anyway, I still have the bottle it came in, with a little left over in it. And I'm looking at this stuff, and I'm thinking it's worth a shot...

(Random thought #2 - Powdered Aluminum)

- Edit -

To give you an idea of just how tiny ultra fine glitter is, I just did a size comparison...

Crystals of table salt are bigger.