hmmmm, I think that if you don't want it as an action to the stuff that is supossed to move in the wind, I'll guess the only way is to animate the models and add an interesting wind noise to give you the feeling that there is wind....
It's all about faking it, when you really want to program it, I think that it really WOULD slow things down much.... However it's an interesting thing; maybe just to mess around a bit someone could combinate clever coding for the wind with the tree-generating code.....(easy when you just animate the model.....)
mmmm I wonder how they do winds in games like Delta Force: Black hawk down .....................