I can't remember if the book said he was bald, but that would be a good way to hide the Reod, by pretending to have gone bald prematurely.
It's also possible that he had a spy or Seon (not his own, if he had one, of course) watch Raoden discover the Chasm line problem, and, having studied the Aons himself after he transformed, was able to send a decoy around while he pulled the strings. Then, when Elantris was restored he could have fled to Roshar, or even been recruited by the Ghostbloods, as Mraize states that they care not for personal morals or allegiances, as long as they stay loyal, after all, having an Elantrian in your group would be very advantageous.