Serfty.
Not sure where North is at Melb Int - but easiest way I can describe where to go is...
Pretend you've cleared customs etc and are walking out of the customs area - Where all the "friends and family" are, turn left. Walk to the end of the hall. There's an information window area marked "Customs Client offices" or something similar.
Ask there about the trial.
There's a basic map here
http://www.melbourneairport.com.au/p...map_window.asp
Click on "International Airport", "1. Arrivals After Customs"
The Customs Offices marked there are a little incorrect - they actually extend over the blue and white and stick out into the arrivals hall.
If you've set it up when you depart, within 24 hours it should be right for coming back.