I will start by saying that I left the mob just over two years ago - so things may have changed.
Firstly, go to local resettlement office and find out your entitlement to resettlement leave.
You may be able to claim a 'work experience placement' with your overseas employer (I did
).
How much annual leave do you have left?
It was surprising just how much time all of this added up to (many months in my case)
Also, speak to your boss - would he be willing to gap your post?
Talk to your desk officer. I had a very sympathetic one who was most helpful.
Will the overseas employer be willing to hold the job open for a few months? If they really want you, then they will I am sure.
Above all, don't take "no" for an answer. Best of luck.