Possible alternative method below - I have a colleague friend who claims this worked a couple of years ago on Qantas although I have never tried myself;
1). Make a booking right through to payment page and then not pay. This generated a PNR.
2). Ring up call centre to pay explaining system won't let you pay online.
3). Ask to pay across multiple cards as you don't have enough credit on any one card to pay the fare outright.
YMMV
