I can only speak from experience in discussion the same topic with a crew member about 6 months ago who wanted to do this. He did a bit of asking around and wasn't able to find anyone who was approved for commuting. BNE and MEL are the only crew bases as you stated.
The "trips" can range from 1 to 4 days I think and there is also airport reserve duty in 5 hour shifts I think. They also have something called "available days" which I think is like home reserve where you could be called in.
If the company wont approve any commuting rights you'd probably have to have a place to stay in MEL or BNE. He looked into the staff travel and you'd get about 25-30 one-way trips for about $20 a trip (fees and charges) after which the price goes up to about $45-$50 a trip. You also wouldn't have access to a staff car park in SYD.
Hopefully someone who is actually
VB CC can provide you with some more up-to-date and, fingers crossed, more positive information.