@DBear wrote:
Not exactly used in this way that you are asking but I understand where you're coming from.
It's easier (in parallax) manipulating the images (or divs that contain them) as these are static elements and you can just increase or decrease there position relative to the document as you scroll (using the scroll distance) As Mark said there may be a problem if the window height changes or other unforeseen changes that may effect the positioning so you have to protect against these.
That being said , I believe it can be done. Using a similar method but you have to plug in to the timeline and manipulate the timeline's current time using information gathered from the "on scroll" event.