The setup is the same as an AOV except we use a light path expression instead of an AOV channel name. Additionally, we can group the outputs by light groups and/or by geometry set up by a lpegroup.
You will find a useful set of video tutorials and discussion of these practices on the RenderMan Community site.
An LPE is made up of tokens which are not the most artist-friendly things. For this reason, we provide a list of LPEs in our plugins that can be easily selected and output. We also provide options on how specific you want to be when it comes to output; from outputting all your direct or indirect interactions at once per type or outputting them per-lobe which provides greater control for advanced workflows.