Wow, thanks for all the advice folks. I'll give Qantas a call, but failing that it looks like I'll be investing more in my SQ membership in the future. Gold isn't worth an $800+ trip to SIN (E.g., QP membership is $380 for non-residents).
As far as getting a mate to fly for me, it's an intriguing idea, the chances of getting caught are minimal, but I agree with the majority that it constitutes fraud. I've seen enough people escorted off planes by the police to not wish that on a friend.
But it begs the question, does this really happen? If one more trip makes the difference between gold or platinum, I can imagine people going for this. Anyone heard of people asking others to take flights under their name to get more points/status?