I actually think the easiest way for you is to just post on the OzFest thread and see who else may be travelling on your flight. You can also monitor the 'May 2009' thread here and see who else may be flying around the same time as you and can guest you in. You may get lucky and go to the J lounge instead of the standard Qantas Club.

QF only assign seats 24-hours prior to departure, no one can pre-select a seat, not even a super-doper-powerful-triple-elite, AFAIK. Nothing is for sure, but registering your preference should be enough. You can also register for QFF just to improve your chances slightly (but only very slightly).