If you would read your Netflix user agreement, you would find that TPB is no more, no less acceptable than Audials as content may NOT be reproduced without written conscent from Netflix. In fact there are a few sections of text forbidding exactly what you're doing with Audials.
So if you're looking for a "legal way", the closest you're going to come to that is one of the following ways:
1) Get a legal streaming service on your Ipad (doesn't netflix work on Ipads? I don't own one, so I don't know) I know that rules out air planes, so you're screwed there.
2) Buy a movie on DVD, use handbrake, but if you live in the US, you still won't be legal if your computer can decrypt a DVD WITHOUT a properly licenced decoder librairy. For instance, libdvdcss is NOT legal in the US. I'm not an american lawyer, but that is my understanding of US legislation in the matter. If you live elsewhere, check local legislation.
In other words, other than buying from the Itunes store, straight to your Ipad, you have a bunch of verifications to do before you can be sure to be legal. Audials, or any stream capture software, IS NOT LEGAL no matter where you are as per you Netflix user agreement.
Lastly I doubt Audials will work as you intend it to under crossover...