How about the center of a cheap plastic fresnel lens? Carefully cut it to the size of the existing lens, and then slip it into the Mag's head behind the regular lens. I'm thinking fresnel lens as in something you'd see in a bookstore on the bookmark rack. I bought one of those a while back for less than dollar. I have idea how well this would work as a diffuser, if it would at all. If I could find my spares, I'd shine my Mag through one to check the results. I have one tightly sealed away in my hiking PSK, but I don't really want to open that up to dig it out.