I haven’t had any experience with attempting to get Qantas to extend the membership year to credit your points to the previous year (so you can reach gold) but I think the chances would be very, very, very slim of Qantas agreeing to it.
In order to get the extra status credits you will need to fly before the end of your membership year.
One option would be to book a domestic return business class ticket in Australia on Qantas. An example of this would be Melbourne to Brisbane return which would get you 120 status credits (enough for you to reach gold) however this would cost over $2000 and in my opinion would be hard to justify just to reach gold.
Considering you would have reached the minimum four flights on Qantas by the end of your membership (a minimum of four flights on Qantas or Jetstar are required per year to move up membership levels) and that you are going to be doing a trip to Asia this membership year, I would recommend looking at extending you stay in Asia and doing a short haul business class trip on a Oneworld partner airline while you are there. An example would be: Hong Kong to Bangkok return flying Royal Jordanian (Oneworld alliance member) in Bussiness class. This would get you 120 Qantas status credits. Royal Jordanian fly their 787 dreamliner on this flight with a lie flat bed and is a quick 2h 50m flight each way. This flight would only cost you around $800! Less than half the price of the domestic flight example above for the same status credits!
You just need to weigh up if gold status is worth the extra $$$. Will you be flying much in your next membership year? If next membership year you will mostly be doing domestic or international travel on Qantas it might be better value money wise just sticking with your normal travel plans and buying a Qantas Club membership for next year which will give you lounge access when flying on Qantas or Jetstar (remember Jetstar is not only the Australian Jetstar but also their sister airlines Jetstar Asia Airways, Jetstar Pacific Airlines and Jetstar Japan so for example if flying Jetstar Asia from Singapore to Malaysia you could use the Qantas Singapore lounge). Don’t be worried that your 100 status credit will go to waste as these can be used to try get Qantas gold next year and will also be used to build towards Qantas lifetime silver or gold status (7,000 or 14,000 status credits). If you are planning on flying Oneworld partner airlines a fair bit next membership year than Qantas Gold is definitely worth trying to get this year to enjoy fast lines and the lounges!
Also worth keeping in mind that it is a lot easier trying to redeem flights when you are a Qantas Gold member so if you are planning on redeeming a flight next year it might be worth going for Gold.
All the best!