Not a problem. There are two ways you can look at this - you can edit your base gradient image to fit your shape, or you can mask it off. In either case, a rotation of the image around a central origin will mean the alpha will be where it needs to be.
How you work your rotation is up to you. Remember that you can declare items as variables and expose on spawn. You can then break them and set specific elements.
Or you can rotate your widget, using an expression of your percentage (as you would with a progress bar) to rotate it. Remember though, that you might want to express this in Radians.
Simple spazzmath should fix this.
I will be doing a radial bar at the weekend. I’ll hit you up with my method then.