Seeing a picture of Frank Gorshin as Bele makes me think they COULD do someone from Cheron. Maybe only a non-Starfleet character like Phlox or Shran (for continuity's sake) has a run-in them at some alien port. Maybe they get killed in a scuffle with some badguy.
I actually had an idea how they could show a Talosian: Valdore (whom I think they need to bring back anyway to justify how he earned a ship being named after him) kidnaps Archer or Trip on some planet. Valdore's also abducted an individual from Talos IV and won't send them back until they cooperate. He makes the Talosian create illusions in order to trick Archer/Trip/whoever into giving up some Starfleet secrets. (Of course the main characters never SEE a Romulan and may or may not see the Talosian) Might be a nice touch if they cast a woman in the role, but dubbed their lines over with a man, as in TOS.