Some comments are correct and some are nonsense. I fly out of Chiang Mai every month I to go to Singapore. I clear immigration in Chiang Mai then I go through a special CIQ lane in BKK. It has been this way for many years.
maybe we are talking about 2 different things. I have secured an LTR based on a company in Singapore. My contract in Singaporean i pay taxes there and work from here. ???