yes, but he will have to leave Thailand to convert to a non-o… and what if he can’t get insurance from one of the 14 Thai companies due to overweight or pre existing conditions? Then he is screwed. Not to mention the mandatory police background checks and elephantitus certifications.
Non O visa is a much better option.
Bank account is not a big deal and an agent is not mandatory at all unless your time is extremely valuable. Navigating the bureaucracy is a good way to start learning about how things work.