<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by thadocta:
One other way to do it is to book through a travel agent, get them to place a remark in the booking that QF have permission to change the booking, and then phone QF to do the upgrades. With the comment in the booking they can then look around at a few dates either side of your ticketted date.</font>
You can also buy a full Y ticket on your preferred flight, and if no upgrade is available, switch the flight and keep doing so until you get upgrade availability.
I've only once been unable to secure an upgrade this way, Darwin to Sydney on the red-eye, but got upgraded at check-in anyway. Works for me - didn't cost me any credits.