Yes. It's possible for ANYONE to open a bank account ... I've done so twice whilst on 30 day visa exemption. HOWEVER - even though it's possible, it's not always easy! Some banks refuse. It's easier if you take a Thai person along.
The questions that annoy me are not "how do I do this" questions, but rather "what will happen in 3 months time" ... sorry, nobody here is psychic and even if we make educated guesses, they'll probably be wrong!
Doesn't have to be a return ticket - can be an "onward" ticket. Book a refundable or very cheap ticket that shows you're leaving the Kingdom within the required time.