If CASA want you to shutdown and feather the prop to simulate the failure, they're going against their own documentation. From the CAAP, feathering not recommended:
Propellers should never be feathered in flight during training below 3000 ft above ground level (AGL).
Finally, CASA strongly recommends that, when practicing asymmetric flight, an aircraft should never be landed with the propeller of a serviceable engine feathered. The risk far outweighs the minimal benefits, with abundant examples of such unnecessary risks proving fatal. If a landing with a feathered propeller on a serviceable engine is contemplated, a
comprehensive risk assessment should be made and a clear plan developed. The plan should include weather, traffic air traffic control and any other factors
But nothing says you can't use the mixture to simulate the failure. It only talks about the throttle being kinder to the engine, which has previously been proven incorrect.
5.5.2 Instructors must emphasise that during a practice
engine failure, when the throttle is closed and the propeller is
windmilling this replicates the situation of high propeller
drag that exists until the propeller is ‘simulated feathered’,
when zero thrust is set. Slowly closing the throttle is
probably one of the methods used to simulate an engine
failure. Although selecting idle cut-off may be kinder to an
engine, the engine or aircraft manufacturer may not permit
it, so slowly closing the throttle to idle or zero thrust is
unlikely to harm the engine and allows for immediate
restoration of power. When setting zero thrust (only after the
student has completed the simulated feathering), throttle
movements should not be rapid, and of course the student
should have been briefed about your actions.