He should apply for a NON-O visa outside Thailand, and then come back in and open an account legally on his own. Multiple entry NON-O visas are not available inside Thailand anyway.
He can find an agent happy to promise the moon and the stars, but even if they’re aren’t lying he risks having the account closed anyway at a later date.
All this reliance on agents is expensive and foolish. Just do things right and save a fortune.
That may not be what he wants, but want in one hand and crap in the other and see which fills up first.