There's a lot of debate on SSN/ EIN/ ITIN on Apple forums and lots of confusion. Now, in the long run I have some crazy ideas but for now...
Go to the IRS website. Download form SS-4 to fax to the IRS. Read the form. See the back where it says "Is a foreign person needing an EIN to comply with IRS withholding regulations" (and for double-taxation treaties etc. eg. Australia) ~ fill out as needed.
Well, that's where I've gotten to so far.
Apparently you can call the IRS direct, or fax, wait a few days, call to check your EIN number, they will send you a letter in a few weeks, then wait another few weeks, then only enter into iBooks Paid system, then sign up, then only submit, wait 1-2 months for approval, etc.
Normally this would dent my enthusiasm but there are no aggregators for interactive iBooks 2... and, as Morpheus said,
"...They are the gatekeepers. They are guarding all the doors, they are holding all the keys, which means that sooner or later, someone is going to have to [ ] them"
There's also a few US Embassy Australia "recommended" US tax consultants in my city so I might have to chat with one of them sometime.