Owen,
Mate J* Vietnam operate HCM-Hanoi (BL- flight code). So all you need do is go YMML-YSSY-VVTS-VVNB.
But the last bit won't be 100% Australian as QF is a minority shareholder (but that's also true of the SG-HN leg in your example).
Not great but it cuts out one leg and one airport wait.