As I aim to hold USD and not AUD I would prefer to make all my trades in US Dollars without the need for any conversions to/from Aussie Dollars each time.

Which Australian brokerage firms allow this? Most that I've checked will only allow you to purchase stocks using your AUD (which they will gladly convert each time). So far I have not found any Aussie broker that will allow me to conduct everything in USD.

Can someone help point me in the right direction?