"My thought was to do the 40 odd hours it takes to convert to CPL(A), sit the exam then find the fastest route to flying vans."
Hmm yeah thats a few $$$ your gonna outlay there, be best to find the fastest way into vans BEFORE you outlay to be sure your prepared to make the effort!!
"...although now that you mention airlines it might be quite conducive to my dreams of retiring to the Whitsundays, sitting under a palm tree and drinking Pina Coladas...

"
Yeah what a great dream but remember you are still gonna need that twin time for an airline.
I do recall a pilot being hired in Hinterland who had a RW background with twin RW experience......apparently that was good enough as far as the insurance company was concerned.......
Certainly be worth a call/visit to them to see if they would do that again, I think they do struggle to find Van drivers with experience though so would appreciate you rocking up with an endo!! Dunno for sure but expect Troppos would only put there more senior (guys who have done time on the rock) drivers on the Van with a CS base??
Dont wanna put you off by any means but if you want the time for that interesting job overseas the whole hour building exercise could be quite time consuming!!
Anyway just food for thought, all the very best with it!!!