How to keyframe opacity on Paint Node?

Is there a Node that I can place after a Paint node to keyframe the opacity of the Paint Node?
The closest I found was using a Mix Node to and hooking the Paint node to FG and my main clip to BG, then I can keyframe the mix value, but I was wondering if there was something more commonly used for doing this.

Thanks for any help!

The Paint Only output can be composited over a background, so you can use this set-up and animate the Composite node’s Amount parameter.

Great thanks Marco!