Have now found a workaround - by creating a custom app
custom_app name DivertCalls
code
; *21Number# for immediate divert at telephone exchange
; #21# to cancel divert at exchange
;
exten => 2100,1,Dial(Zap/3-1/#21#)
exten => 2101,1,Dial(Zap/3-1/*21YourPhoneNumber#)
this at least will allow access to Australian exchange codes, I will work on expanding the app to include user specified divert number later.