Arrrgh... Up in Sydney, the regular Caltex/Woolworths servos do NOT offer ANY discounts on LPG 'at this time' (as per the sticker on every LPG bowser).
I did come across one at Seven Hills - but that's enough Km out of my way to make it questionable value.
Nevertheless, even with a slightly worse fuel economy (litres/100km) at even the higher prices, it's still got petrol beat!