Maybe a Round The World Ticket is in order.....
By routing back via the US, there should be savings to be had on the fare and not too much additional time. Also, the oppotunity to have a nice break on the way back. Route quickly back SYD-LAX/SFO-LHR-BRU on UA, with LHR-BRU on bmi.
Add more stops for extra points/miles.