Oktas8 and Rate1:
A check of the current CAR's (1988) will show you that the requirements for ICUS include at CAR 5.40 (1)
(e) the operator of the aircraft permits the person to fly the
aircraft as pilot acting in command under supervision; and
(f) the pilot in command of the aircraft is appointed for the
purpose by the operator of the aircraft.
One assumes that all the Captains of your operator are approved for "the purpose". And there should also be clauses in their Ops Manual dealing with gaining the approval.
The GA companies that I am involved with have exactly that in their Ops Manuals including specific training requirements for the supervisory pilot. CASA involvement is not required in the training or approval process.
Blackburn