Another update.
Got the stuff from America however it' just diffusers and not a perspex panel - my view is that a perspex panel is needed to retain the correct placement of the diffusers so out with the dremmel.
After a couple of hours of careful cutting / sanding / milling it looks like this. I used varying grades of wet and dry on the perspex to get it as near to opaque as possible whilst retaining a smooth unscratched appearance. By placing the diffuser in front of my perspex piece, the sanding marks are not visible.
My panel is above, the diffuser is below. I've yet to see how it looks in the car in terms of bright spots but in all honesty, I could care less, i just want rid of the ginger!