Since firmware updates are provided over the air by the carrier, and Telstra, AT&T, and a couple EU carriers are the only one's who officially support the device. I don't really see any option but to take the device back to Austrailia and try to do an OTA update. This may require the use of a Telstra SIM and APN. Publically, at least, Netgear seems to be refusing to provide firmware or a tool to update it. I had heard rumors of the launch of an unlocked commercial version of the MR1100 -- which presumably would require Netgear to provide direct support -- but I've not seen any official announcements to this effect.
There is a way to get admin access. Login to web interface as root/admin. Download existing configuration (System tools -> Configuration file and click on Download configuration file). Open downloaded file with text editor. It depends on you firmware version whether configuration file will be encrypted or not. If your text editor shows XML data then just search for root or X_HW_WebUserInfo and modify existing records or add a new one.
If you own devices with wired-only (Ethernet) connections and your router or modem is too far away or your wireless network doesn't cover enough area in your home, an old router can solve your problems. By installing the free DD-WRT firmware on the old router, you can turn it into a wireless bridge or repeater. This means that even devices that can't reach your main router can get connected through the old router anywhere you put it.
There are a few different scenarios here, but for all of them, you'll need to install the Linux-based DD-WRT to replace the old router's default firmware--and give it not only more options but also enhance its performance. Head to DD-WRT to find out if your router model is supported and download the latest release. If your router can't install DD-WRT, you can always buy a used one, such as the popular Linksys WRT54G for pretty cheap.