I have not found anywhere in Scrum.org how this is possible. You have the trainer form sm, po, dev. how about nexus? is this maybe included in the SM TTT (Train the trainer program)?
Currently I am working in a SAFe orgnazitaion as a supportive transformator coach or something like this. BUT what I found is that for mid sized organizations or even from 3 teams nexus is much much better.