Alpha fade on edge of scroll box – possible?


I have a scrollbox full of things, and I would like the edge of the scrollbox to fade off to transparency – is that possible?

Here is how it looks:

Here’s how I want it to look:

If the scroll box was on top of a uniform colour, I could obviously place a gradient on top of it and it would fake the effect. However, this widget has an animated background, so that’s not possible.

Anyway know if there’s a way to do this?