Very easy, you just have to invert LON/LAT values:
SELECT AsText(Transform(PolygonFromText('POLYGON((151.110971 -33.917172, 151.112495 -33.916443, 151.113276 -33.917637, 151.111512 -33.917783, 151.111577 -33.917253, 151.110971 -33.917172))',4326),3112)) as result
result:
POLYGON((1569305.481332 -3926985.759663, 1569455.307825 -3926925.091727, 1569508.606645 -3927065.382207, 1569345.639225 -3927059.314561, 1569359.502478 -3927002.182676, 1569305.481332 -3926985.759663))
http://en.wikipedia.org/wiki/Well-known_text
POLYGON(x y) = POLYGON(lon lat)