You can not create complex networks inside the graph, Hopefully in the future LKDX will talk seamlessly to BF.
For now, you can do a few things.
https://help.autodesk.com/view/BIFROST/ENU/?guid=Bifrost_Common_apply_materials_html
https://www.youtube.com/watch?v=dhSfBibzNbs
Also, you can do it through USD and if not you can always create your materials in the hypershade and drag and drop them inside the graph, and use userdata nodes to grab attributes/properties. Those are the ways for at least right now.
You could also use Arnold operators if you want.
Apply the materials first and use USD.
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