The MEL-PER portion of the trip is a domestic flight so an upgrade cannot be waitlisted. You can continue to look for availability (it does change) and if it pops up the snag it. Otherwise the only option is an On Departure Upgrade that can only be done at the Qantas Club lounge so he will need to have access to the lounge in MEL.

To get the Qantas booking refernce, call Qantas Reservations and you will need to know the passenger's name, flight details, date of travel etc. They should be able to provide the booking reference.