The problem is most SQ F cabins are unavailable as *A redemptions. That rules out buying a brace of miles from US and using them to fly SQ- though one might be able to on a regional route like SIN-CGK. (The other problem is if SQ doesn't make seats available until close-in it gets hard to plan much- you will have to grab them on the fly. And 77W won't be available in F as a *A redemption.)
OP- SIN-HKG? I know a 77W does SIN-HKG-SFO...