Here's a little tip for anyone trying to devise a screen blanking system... Read cheap or possibly even free.
Go to your Information Systems department and ask or buy any junk hard-drives or older smaller ones. Get in there and rip it apart, take the two magnets, top and bottom that control the swing arm assembly. On most of the drive's I've gotten into, these are the shape of a kidney bean and have two drilled holes at either end, perfect for screwing into crown molding or anything you desire.
I've been able to support about four pounds on just one of these little guys.
If you've already got a 16x9 metal frame, consider cutting 1/4" ply or some other light board, wrap it with black velvet and use it to mask a 4x3 frame.
I'm currently working on a project with a 1"w x 1/8"d x length piece of metal, that has been screwed to the wall. The masking attaches to it via the magnets and allows me to frame the screen down to the smallest adjustment. This is even better since I can't control keystone on my projector and am using this to kick out the corners to adjust for the screen size.
This would be a cheap solution for anyone using a painted wall or any type of frame that, well - a magnet would stick too.