500 Multi command is a CAO requirement for RPT mulit-crew command above 5700kg's. So you will either require your employer to get a dispensation from CASA, or a hell of a lot of ICUS before you make command. Either that or you can be a permanent F/O.
See CAO
82.3 for more details.
Cheers, HH.
PS: I suspect you are not the first to follow this path, so keep asking around someone who has been there before should be able to help!