Thanks to a wonderful agent who tried different routes, I was able to change my ticket ($55) charge and stay within the MPM.
I'm flying HKG-SYD via SIN, (openjaw) MEL-SIN-KUL-BKK (stopover)-HKG on SQ and TG.
It's great. I only have to get an extra ticket from SYD-MEL instead of getting a BKK-KUL rt ticket.
What's there to do in 24 hours in SIN and KUL?