[DSilk]

You cannot use the ventilation system to heat your M3 while it is parked, as the system is set to vent hot air out of the car. The only system available to heat the cabin without the engine running is the residual heat function that uses engine heat to warm up the cabin while the car is sitting. That function only works if the engine is already warm. Cheer up. Sydney's climate can't be that much different than Miami's (albeit with reversed seasons), so you shouldn't be dealing with any really cold weather.