AFAICT, there is no OW service ex-RDM. There are codeshares for AS, DL and UA. Seems to me that the easiest way might be to get yourself to YVR, then plan from there, starting most likely with CX YVR-HKG-HAN. HAN-BKK on OW will require another HKG transit. For BKK-HKT, check one of the several LCCs in the area, FD, PG or DD. For your return, there is CX/KA service HKT-HKG.