Thanks for your response. I apologize if my question wasn't phrased clearly enough. I want find a trigger based on whether someone uses a mouse wheel or touch pad to scroll. I don't need to know where in the window or document the current position of the document is--that is, I don't care about detecting the scroll position.
The first hurdle I have is to see if I can find a "trigger" based on detection of mouse wheel scrolling or trackpad scrolling. Perhaps it's not possible and I need to trigger using hot keys: for example, the other alternative is to use command+shift+down arrow as a trigger. Again, I believe I can handle the scrolling part (and someone already suggested "Simulate Scroll Wheel").