I was thinking on the same lines of deadflowr, but I wanted to try it before suggesting it. Well... I tried it and it works. It looks like the Hidden=true is the mime type that controls the display of an application. I tested it with NoDisplay=true and it did not work.
Just change it to Hidden=true and you should be good to go!
Comment[en_US]=Wallch Wallpaper Changer
Comment=Wallch Wallpaper Changer