Doesn't 5.40 (C) say that you do need an ATPL to log ICUS on operations that require an ATPL?
Nor do you have to have an ATPL if the aircraft requires one to be in command to log ICUS.
(c) if the person proposes to carry out an activity for which a flight
crew rating is required—the person holds a flight crew rating, or
grade of flight crew rating, that permits him or her to carry out
that activity as pilot in command of the aircraft concerned; and
I suppose you could interpret it as saying that the Supervising pilot is really in Command and therefore covers it.