Prosmart, it's very easy to get a tourist visa from the US. Just apply for the ETA on immi.gov.au - it'll give you a tourist visa that's valid for a year but only allows you to stay three months at a time. There are no questions about why you want it on the application - it takes five minutes to apply for and costs $20. Getting a tourist visa is much easier from a low-risk country than from a high-risk one.
Just make sure you are approaching this as a *holiday* (key word) with your partner for the next few months. Make sure you have plans for things you want to see during your holiday. It really isn't a big deal... they probably won't even ask you anything, just wave you on through. One tip, though: DON'T bring a CV or any other documents that will make them think you might try looking for a job while you're there. Even if YOU know they're for after you get your PMV, carrying those things with you while heading over on a holiday isn't a good idea.
Many, many people on this board from the US have done this and none to my recollection have had any trouble. You just need to let your CO know you're doing this and ask them to please let you know when they're ready to decide your visa so you can get offshore. Then, near the end of your first three-month stay, you'll need to fly out (Bali, Auckland, wherever you want), spend a few days, and then fly back to Australia. You shouldn't have a problem. Make sure whenever you're heading offshore you give your CO a heads up, too, so that hopefully she can grant your visa on one of those trips (if you're lucky) and save you that extra flight out.
Here's the thing: As more and more couples are separated for long periods of time, Immigration officers are actually sometimes recommending that couples use tourist visas this way to be together. But *technically* tourist visas are not for the purpose of waiting out a visa together. They're for holidays. So... approaching your trip there as a holiday is what you want to do. It's silly - Immi really needs to fix this and just publicly allow couples waiting offshore to visit each other this way while they wait, OR fix processing times so it's not necessary. But for now, it's the only way to do it.
Also, the idea that doing the above can have any effect on your PMV is rubbish. Even people who have illegally overstayed their visas (which you won't be!) can still apply for and be granted partner visas like the PMV. Using a tourist visa and abiding by its terms and conditions (which you will be) is nothing to worry about.