I'd go with the satin scotch tape option for a quick trial route. I also use this diffuser film that I purchased from member waynejitsu on CPFMP. That works even better due to the film material being self adhesive so it's reusuable. If it gets dirty, just wash with soap and air dry, then reapply. There is no tackiness to it. Just needs a clean smooth surface for application. I think it was once sold as some protective film for palm pilot screens. It has a satin-like texture.
I found the link: diffuser film
I'd contact him to see if he has more. This stuff works awesome with an optic as well. I have the Lowe's task force version, which is essentially the same light.