I don't think there are many male Australians named
Elizabeth, or
Elisabeth. But if he had a particularly distinguished female ancestor, then perhaps using her name might make sense. In the time of
Queen Anne, she was godmother to a boy baby, son of a member of the nobility, and he became Lord
Anne Somebody, so it can happen. Or it could. Middle names can be kept confidential more easily than first names; but someone will always find out. I was at school with, as we all thought, an
Alison Margaret. But I got to carry piles of lists for a teacher one day, and it turned out that she had a second mn: Honeybun. I didn't tell anyone else - I liked her, we were friends - but I did mention it to her!