So the two Physics GREs are being offered Oct 09 and Nov 13. According to the ETS website, they claim you can get your scores by phone earlier than by mail if you are willing to pay a fee and that the October test scores can be had by this method on or after Nov 8. http://ets.org/gre/subject/scores/get
In theory, it seems that you could register for both tests, take the October test, get your score before the November test and then decide whether you want to take it for a second time or cancel it and keep your October score. Of course, this means you pay for an extra test and that you will have to study for the November test as if you plan to take it, but in principle it should be possible. What I am interested in is whether someone has actually pulled this off and if there were any hang ups in the process.