Blizzard has made this impossible with the launch of Mists of Pandaria. When they introduced vignettes, the old cache system went away and none of the previously-existing rares were updated to use that system.
What I've done, personally, is turn on nameplates and set them to always show. Another option is to use a targeting keybinding, which you'll find under the WoW client's keybinding menu. Unfortunately, that entails constant key-mashing.