Greggers,
I tried to match as closely as possible to what the vid was doing. I did actually download those high res images from poliigon as well. Cool textures!
Hope this is what you were looking for. Basically, you create an Octane Override for that specific shader and it populates the nodes for octane. That's where you can start adding your octane glossy and mix materials. From there you add image textures and displacements, etc...
Take a look at the file. Someone may have a better way of handling but I think this is the only way I can get close.
I think C4D has more capabilities of handling/changing images than the modo plugin. Looking at that vid, he was able to really tweak a lot of parameters that I just don't know how to do in modo/octane.
Good luck.
https://www.dropbox.com/sh/w8rm5cxf7qu18fr/AABsK5DA7SEDof1j0suYxpY5a?dl=0