You can join the QF scheme and avoid the $82.50 fine by giving a non Australia/New Zealand address when joining. If you have any overseas friends then use their address
I would suggest the AA frequent flyer scheme over the Qantas one; you will only earn 50% miles for the SYD-BKK-SYD flights, however the points are worth more than QF points ( e.g. 20k points gives a r/t eceonomy ticket from australia to anywhere in australia or new zealand. ) plus you will not get stung for large fuel surcharges when redeeming awards. The AA scheme is free to join and you can enrol at
www.aa.com
If you are taking any other OW airline flights within 3 months, then enrol for the AA Gold Lack-Of-Challenge and you'll get OW Ruby status after your next flight ( even CBR-SYD would do )
Dave