Trigger when Scrolling Down

How can I trigger something when I scroll down in my ScrollView?

I try with this but only trigger the message when I reach the top of the Scroll:

<WhileScrollable ScrollDirections="Down">
    <DebugAction Message="Scroll!" />

There is presently no way to trigger on relative scrolling, such as scrolling down a bit. It’s a feature that I hope to get to soon.

Any word on this?