In my eyes the most appropriate way to get your CPL from an RA-Aus background is to convert to a PPL and work from there. The RA-Aus pilot certificate with passenger and cross country endorsement is very similar to a PPL. But you will have to get used to the aircraft, complete 2 hours instrument flying, demonstrate your ability to fly navs, handle controlled airspace etc... Then you can work towards your CPL once you've gained your PPL.
I haven't really heard of a percentage conversion, i.e 1 RA-Aus hour is worth 50% of a GA hour (example!!). By the time a person has achieved the certificate with all endorsements to convert they would have a very minimum of 40 hours, which in reality if taught properly is not possible. I have my certificate with no additional endorsements and I have 35 hours. (Basically in GA terms it's less than a GFPT)
-Andrew