How to export several render outputs at once? I want to know if it´s currently possible in Blender 2.78c/higher to render an image and then get the imge itself as well as the AO pass as two output files (.png) without having to switch to the compositor, change the output node connection from "Image" to "AO" and rerender the whole thing?

For I need the AO as a seperate image, but don´t want to render everything twice... (2 hours each).

If there´s a simple method/script I don´t know about please let me know! 
Thanks all of you beforehand.
I'm using this setup as addition to the normal path and filename for the composed image: