@UIGuy, that sounds like a fairly simple thing to actually make. What you really only need is the position of the individual element and the position of the scroll view, then you can calculate how far from the visual center you are, to do "your thing".
I think from NGUI's perspective, the best thing would be to make those values available in an easily digestible manner, so custom implementations could be based on those values, instead of the specific solution you suggest in your picture.
I'll mull on how this can be done in a nice manner, but no promises (I'm on summer holiday, I'm just bored right now..

).