I have been told that this is possible for miles on board. Not sure about cash, and when I asked about it was told that a) they were full in J and b) none of the crew knew how many miles it cost, only that it existed.

One of my slight peeves about Skywards is that it's not always easy to find information yourself without asking. The web site, for instance, seems to have information but it's organized oddly. Award tickets, for instance, are not necessarily by region but by number of stops, so SYD costs 125,000 miles in Economy from Singapore, but a nonstop destination like MEL costs only 45,000 (numbers might be wrong and are for demonstration purposes only). I understand this is because SYD requires backtracking, but still, what a crazy differential.