Just today ive had success with an option on 2-4-1 return flight.

2 weeks ago i snapped up 2 F seats LHR-SIN in Feb next year on wifes 2-4-1 voucher.....booked outbound only and would wait for seats to open up 2 weeks later and book them.

Nothing else has come up since then as checked daily out of interest....logged on last night and saw 4 F seats from SIN - LHR on 24/2/15....it was 0045 UKT so no way to add to wifes 2-4-1 and didnt want to chance losing them.
Decided to book them using avios and call Exec Club in morning.....booked 2 F seats at 210k avios....just as well as other 2 went when i logged on at 6am.

Called Exec club 10am and only way they could do it was to release seats then grab them (rep was great help and said used to be a problem but since updated systems the seats go back into the pool of seats immediately). I said go for it.....released them....then got them within 30 secs of refunding me ££ and avios. Then assigned them to wifes 2-4-1 voucher and im good to go !!!

Does help to check all the time and ive had success with this method this am.

just thought i'd share