http://www.youtube.com/watch?v=PpNGnkH6Wfg#Don't know how to make your own shader? Look here:
http://ugx-mods.com/forum/index.php?topic=4174.0 !
Or as a backup:
http://codepad.org/klOk9iFgTo enable/disable: press Aim Down Sights and Use Button (might require you to hold the buttons for like a little bit).