Rendering Ambient Occlusion onto alpha instead of white I am attempting to render a surface and it's AO shadow in a way where the darkest parts of the Ambient Occlusion remain, but the light portions are faded to alpha. What is the best way to do this?

For reference, I need the light gray in the image below to be replaced with alpha. Don't worry about the object casting the shadow, it is being protected by a mask.
Just figured out my own question. It seems like the best way to do this is to Bake AO, then use a color ramp node to get rid of the white and adjust the transition.