I use Windows 8 and its region setting is set to Australia. The current short date format is d/MM/yyyy. e.g. 27/03/2014. You may set this as you want without changing the region. Is this what you mean? "Region" is in Control Panel. If it's not what you want, please let me know details more.
Would you please try this?
Go to Region - Click "Language preference" - Click "Add a language" - Add English (Australia).
On my system, English (Australia) and English (NZ) show different things on "Language" window. On English (Australia), it says "Keyboard layout: US + Date, time and number formatting" whilst English (NZ) says "Keyboard layout" only. It might be related to your situation. If my hypothesis is correct, adding Australian one will resolve your issue by adding new formats.