you cannot do theory exams for commercial/atpl outside Australia/ASL examination centres.
it's not really rocket science converting ICAO CPL to CASA CPL and with some 'homework' it shouldn't take too long trip to Australia either. It mainly depends on doing ARN application, then medical (which can be done abroad), especially Initial Class 1 takes month or two to process.
Human factors and air law either heli or aeroplane for converting CPL, passes in those, meeting CPL issue requirements (pretty easy and if you hold most foreign commercials, can meet Aussie total/training/solo/solo XC for the VFR CPL), flight test.
One other 'hassle' is having to file for ASIC before submitting paperwork to CASA. It requires some tedious docs providing and around 200 bucks for 2 years. No real way around it; there's more basic ASIC equivalent for specific airports, but still similar paperwork.