You will mhave to return to Australia to some place other than MEL (such as SYD) and the buy yourself a separate ticket SYD-MEL. And then to use your 4 Australian domestic segments, you will have to stay clear of MEL.

If you want to use MEL as the hub for you 4 last domestic segments, then start somewhere other than MEL. For example, if you purchase a separate ticket MEL-SYD, you can start your DONE4 from SYD. Then return to Australia into MEL (not through SYD) and then take your 4 domestic segments such as MEL-PER-MEL and MEL-BNE-MEL later. The final destination does not have to be SYD, as the ticket can end with an open-jaw. But you cannot go back through the starting point, which in my second example is SYD.