The gesture is pinch, so unless you are trying to use two fingers on your home screens (why would anyone use two fingers on the home screen anyways?), you shouldn't be activating it at all.
And to answer your question; no, there is no way to turn it off. Shouldn't be an issue as long as you aren't trying to use two fingers on your home screens.
On a side note, if you are on your default home screen and hit the home soft key on your phone, that too will activate the screen previews.