You can do it online by searching as a multi-city like this:
View attachment 354125
The important caveat is that the "connecting flight" you add for the second leg
must depart on the same day the last segment of the first leg
arrives (though this
can be after midnight on the next day as long as the inbound flight before arrives after midnight, and connecting flights can go into the next day):
View attachment 354126
You can really get creative (I've managed up to 6 segments before for 20K on some searches), but here was trying to maximise flights on the 330 and I actually need to be in Adelaide that week so went with that as the final destination rather than something more convoluted.
Also important: you can't fly through the same city twice, or it will reprice as 40K, e.g., SYD-PER-SYD-ADL, but via MEL is fine.