Despite BOStonTravels proper response; the way to do it would be to buy a new international ticket with no intention of using it (you can only access the lounges with a departing BP); that said, the cheapest OW ticket you'd probably find would be RJ to HKG (one flight per day), however I have no idea how you'd clear immigration after going through connections. The Bangkok Airways lounges are no CX lounges however more quiet than the terminal. I'd just deal with it.