Controlling Lens Flare rotation

So the default lens-flare rotation behavior doesn't feel right to me and I am looking for a way to override this with my own function, something that halves the rotation speed or something.

Anybody know a way of how to achieve this?

Also, I'd like to increase the overscan where the lens-flare still gets rendered when then camera not directly looking at it, because it has a relatively big glow component and it looks odd when it suddenly fades in.