wow this is awesome! Def going to have to try it out on my GC! They don't make any good diffusers for them!
EDIT: oh and for all of you that can't find the board that the OP used for his; it's just simple thick poster board. Lol go to the school supply section of either Wal-Mart of Staples/OfficeMax and grab some. All sorts of colors. I'll probably use black so I don't have to use a lot of undercoating.