Even before today's strict KYC and anti money laundering rules, I doubt you would be able to open a bank account online here in Thailand.
I know in the west, some of the online banks allow it, but they require strict identity proof.
I don't think Thailand is anywhere near ready for that yet. But good luck with your search.
Asfor using some online entity or an agent. Would you really want to risk losing all your money like that?
Pretty sure you would be breaking many of the bank's account security rules about ensuring no one else accessing your account.