The first DC didn't involve any human people, only puppeteers and trained technicians in puppeted costumes so there won't likely be any extras. However, they did have a "little person" for a few key wide shots. I believe that Farscape was shot in Sydney and POTC is reportedly using the same team so that would be my guess too. I suppose you could apply for an internship or production assistant. I’m not certain how that works in Australia or if it requires guild ties. I have a feeling that this is going to have a very lean crew of people working in controlled environments.