Get some Darkened Lexan plastic, or Clear and paint it black. About this size 3'x3'x1/4. Now lay the photoetched fret on top this Improve's Visability 100%, With your Hobby Knife you can get very close, And cut right at the edge. The static from the Lexan helps hold the piece down Most of the time. While you are cutting.
I was working in a laboratory last night and saw some rolls of stuff called GRIP LINER to put on cabinet shelves. It is spongy and sticky like those little rollers you use to remove lint and such from clothing and then just wash it off. There was a warning label not to lay it on some wood finishes very long it, would hurt the finish. I don't know what it would do to a painted part. It would also certainly keep small parts from flying away. This might be found at Wally World!
I bought a roll of Grip liner at Home Depot while getting some items. It was under five bucks four a four foot by eighteen inch roll. I got a roll that is white with squares embossed in it. Maybe the lines will be useful.