OLCI should probably work. It has worked for me last 2-3 trips this year. IME, BKK security accepts a mobile BP on device (sometimes NH will not issue a mobile QR BP, it has in the past but not for my last trip a month ago) or a printed pdf (NH only provided this, and not a mobile QR, my last trip). If you do OLCI, make sure to get to gate a little earlier to complete doc check. Alternatively, go to the transfer counters airside when they open at 3:45am - they can perform doc check as well.

Of course YMMV - rules can change.