This is mainly to piss people off (and believe me, it does).
Just when Wintergrasp is about to start, get yourself invited to the raid group, then create a portal to any city on the place where the Wintergrasp portal would appear. People will click it like crazy, and find themselves teleported to another city.
This, also works ofcourse, if, for example, your main is alliance and you so happen to have a horde mage on the same realm, to give the alliance an advantage in numbers.
Some of you may call it common sense, but its evil nonetheless!6):