How many VS miles do you have? I can't help but think going to HKG is inefficient. For example if you had 210k (I'm assume you have 180k for HKG J x 3) you could book IST-SIN-IST on SQ and then use 120k avios and modest cash for MAN-IST.

Otherwise the obvious thing to get more value from your Avios is to get a BA PP Amex and earn the 241. Even if that took you beyond the April changes I think you'd still be better off. No avoiding the cash costs there though.