Yeah unfortunately only option at that point is to use an agent. Thai visa center does it (they're in bkk but can do the extension for you anyway) not sure what they charge right now. I'd send them a message.
I'm sure people have been, I just haven't seen any. Normally though in that case the embassy just asks for additional documents , weird they would deny him unless he was unable to provide 6 months after they asked for it.