To be honest SG I had a few of these frames spare, so I just nicked a pane from one of the other frames as a test. I had thought of using acrylic but didn't know if it would look as 'pure' as the glass.
The one cut from card doesn't need the extra glass to support it and is just jammed between the existing glass and the front of the frame. I never got around to experimenting further with these ideas. I like yours though, especially the nice glossy effect of the printed metal. Great idea.