I got a non-O visa from London at the end of January this year. I keep 800,000B permanently in a Thai account for this purpose. A few years ago I tried to prove 65,000B / month income but that proved impossible.
All round it's pretty daft and unnecessarily onerous but Thailand is what it is and it's best to give them exactly what they want if you don't want to waste your time and money.
I'm no expert but it seems to me there isn't a way around this one.
BTW If you are planning on extending it is worth trying to get your TM30 sorted reasonably soon after your arrival.