Sorry, it's pretty clear that there is no loophole. The rules for AA PLT say
Originally Posted by AA Platinum Guide
Benefits of Sapphire status include access on the day of travel to the Business Class lounges of all oneworld airlines when you are traveling internationally*...
* Lounge access not available when travel is wholly within the U.S., Canada...
Internationally in this context doesn't mean on an international flight, it simply means outside of the U.S. (and Canada, Mexico, etc.), so you ought to (and do) have lounge access on domestic flights within Australia, the UK, Spain, Chile, Peru, Ireland, Finland, New Zealand (and soon Japan and Hungary; did I miss any?).
The Qantas admission rules are moot both in practice and in (the hypothetical) court; since it's AA who have to pay for your lounge use, it's AA who decide which lounges you can use, and AA never promised OW lounges on US domestic (+ etc.) itineraries. To the contrary, they go out of their way to point out that you don't get it.
Michael