Yeah I'm unaware of any premade addon that does it. That post Wubsie put is exactly what I would do, it wouldn't take much more than creating a tiny addon with a toc file and a lua file, where the lua file contents are literally what is in that post, but you change the spell names in the "SetAttribute" lines and the 'key'. Easiest way would probably be to make one addon for each class, and only enable it on the relevant toons.