Wowhead.com has now made a .js that'll do most of the work, I'm pondering how one could potentially integrate these two. Wowheads version requires the users to input either a link to the item or the itemid trough the vbb implementation one of their users posted on the forums.
However, mixing this hack with the .js might just solve that as the .js from wowhead generates the correct tooltip (which looks a tad smoother then the one from this hack, rounded corners and everything ;p) and doesn't really need an itemcache.
Being able to just do [item]Perdition's Blade[/item] and having that trigger the .js would be downright cool

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