Following from private messages and general comments, I have attempted to flesh out the instructions in greater detail, but please let me know if I'm needed to elaborate or include additional images for your convenience and understanding.
I've decided to polish my original guide for this method and give the instructions its own post because not everyone will see where I initially described the process. This method has been vouched for by a number of members in this community, and is safe to use.
Please note: This guide will effectively show you how to purchase any game via the Origin client for a significant discount, I am simply using Battlefield 4 + Premium as an example.
By using this method, you'll effectively be paying $50 / $40 respectively in AUD for the two games, and you'll also be going through the actual Origin store.
This method requires us to pretend that we're from Mexico, and we're going to do this via a process called proxy.
Download this. This is a standalone client which will allow us to pretend that we're from Mexico. It's the first box you see which says FlyVPN Client
Input the free username and password as supplied by the website, it's on the right-hand side of your screen as indicated by this image this combination will reset over time, so please check thoroughly.
Once you're logged on, find the server for Mexico, highlight it and press the giant blue button that says connect. You're now from Mexico. This step may take a while depending on the capacity of the server. I can guarantee you that if you're patient enough (if you keep pressing "Connect"), you will be able to connect.
Type in origin.com - You should now be directed to the Mexican website, so everything will be in Spanish. Use Chrome to translate everything, or your preferred browser to translate it to English.
Search for Battlefield 4, or premium, or both. Add them to your cart.
Keep pressing the buttons until you get to the absolute end where you have to type in your Origin ID + Password. So basically, put it in your cart and then press the button to process it.
Turn FlyVPN off. This is absolutely essential. Turn this off before you type in your Origin ID + PW.
You're now back in Australia, type in your Origin ID + PW.
Fill in all the prompts correctly. If it asks for your address, put in your correct address. Don't put in a fake address, no fake anything. If you put in anything that's wrong, or says that you're in Mexico, there's a chance it will just place an authorization hold of $1 on your bank account which won't clear and will be refunded after a period of time.
Fill in your credit card details correctly.
Press purchase. You should instantaneously have the game in-client, and also a confirmation e-mail to your account. Your Origin client should had a similar record like this one.
What happens when you get a game that doesn't have English included?