A couple of years back I had triggered my 241 and was waiting for it to arrive. I could see the availibilty I wanted (2 x F - LHR>SIN>SYD>SIN>LHR) and called on the off chance they'd hold the seats for a few days. A very kind man said he would hold them - I think he said it was for 5 days - gave me his extension and he kept in touch until the voucher arrived which was within a day or so.

I only post this because from memory it was accepted knowledge then that this wouldn't happen and so I guess it might be worth a try now.

Good luck.