Just to provide some closure:

Managed to redeem two separate tickets:

QF F SYD-HKG + CX F HKG-CDG
QF J SYD-HKG + CX F HKG-CDG

I'll keep calling for the next 300 days and see if QF will open-up another F seat but otherwise, I'll be in QF J while the girlfriend enjoys F.

Thanks very much all for your help!

Now ... if only QF would let me redeem LHR-SIN ... everytime I enter credit card details it tells me that they expect 2-40 chars. in the address field. I'll have to give them a call tomorrow.