Go and extend. Go to Vietnam etc. For a few days go back, extend. I've been to 30 countries in the last 5 years on one way tickets and I've never been asked to show proof of an onward flight. I have about 6 or 7 times used best onward ticket but I havent had to show it. Maybe once, but I cant recall.
Yeah well tell that to the 1 million people working remotely in Thailand. Go to any hostel, you'll see 10 people plugging away on a laptop. Police, goverment doesnt care. Tourist dollars.