Taipei Economic and Cultural Office in Thailand,
20th Fl., Empire Tower,
195 South Sathorn Rd.,
Tel: (002-66-2) 6700200 Fax: (002-66-2) 6700220
I just did a visa run to Singapore and got a visitor visa, which I can convert to a resident visa on the basis of my Taiwan work permit. At the China Airlines check-in desk in Singapore, I was asked to show a return ticket to the UK! I showed my work permit instead, and that was OK. So if you have no evidence that you can convert to a residence visa, you should have a return or forward ticket, or they might not let you on the plane. If you are refused entry, the airline is held responsible. You had better ask the TECO in Bangkok to make sure.
By the way, I think Singapore is a pretty good place to go for an R.O.C. visa.