Thanks for all the suggestions. Unfortunately, all the cheaper alternatives I've researched end up chewing up a lot of time.

We can get the PG airpass for BKK-REP (at a not-so-good time), but REP-LPQ has no seats in the right fare bucket and the flight LPQ-HAN is sold out. I guess I could ask my TA to look at REP-PNH-HAN.

Hmmm...no route REP-PNH-HAN on airpass, but there is one REP-VTE-HAN I've asked my TA to investigate. No luck on that one either. Drat.