Using a multi entry tourist visa and extensions will get you the closest to what you want. On the end of the extension you border bounce for another 60 day stamp. You can do that like 4 times I think.
"Expedia Trick"... Expedia has free cancellation within 24 hours with 100% refund. Tickets to Rangoon, Myamar are like $50 USD from BKK. Book the flight. Print the documents. Cancel the ticket. Boom done.
I've traveled numerous times on a one way only. If you are really worried here is a trick to help... Expedia website allows for 24 hour cancellation on flights with no fee. Book a flight from BKK to Rangoon (currently that ticket is $50 USD). Next print everything out. Then immediately cancel the flight for no fee and get 100% of your money back. Problem solved.