ok I'm not that much up on this but the way I was told U do it and the way I did do it 4 years ago.
U can't get the bkk bank acc or retirement visa outside the country so ...
I was told to book a 30 day trip and before the 30 days run out I would have to sort out a bkk bank acc and a retirement visa all of which I did.
So I bought a one way to Thailand and a one way Cambodia ( 4000b at the time )
I knew I wasn't going to Cambodia so I didn't care what their laws were and all Thailand wanted was a flight out in 30 days so I just threw the flight away once I got my visa