CooldownIcon visual timer filling up instead of running out

[qwertyui]

At the moment CooldownIcon shows the icon as the cooldown is running out, rather than filling up.
I want to see it fill up instead, the way spell cooldowns do on my button frame.

Think of it as reversing the timer fraction, so that it startes from 0 and goes to 1.

There is no obvious way to do it in the UI, so i'd appreciate some help