I already wrote about this on wowhead forums but no activity, perhaps someone here knows the javascript inside out and could help.
Thread:
http://www.wowhead.com/forums&topic=194708
Basically I am using $WowheadPower.registerItem(...) after the window has loaded, to inject items in the cache of the tooltip so it does not have to load it from wowhead servers. In essence, I store the tooltip the first time I see it, after that it gets the data always from the server I am running, saving bandwidth between client<->wowhead and server<->wowhead.
Any tips? So far it does not work, the item I mouseover just says "Loading..." and nothing happens.