Just called up an old mate who flies with Strategic and he says it wasn't them. They were busy doing another ADF charter from LEA to AMB apparently.
If I didn't know that the Skywest A320 was firmly against the fence in Melbourne I'd have thought maybe that was the only other choice, as Jetstar & Tiger seem to steer clear of those charters. But I guess if it's a matter of integral stairs then it could only be Skytraders as I understand they had them fitted in the A319 for the Antarctic ops.