Exchange And Office 365 Calendar Sharing... An Idea

Good evening,

quicklly the problem: the secretary of my manager should manage his Calendar.

She's using O365, he's using Exchange and for the current configuration, that calendars are not sharable directly.

I had that idea... as my manager has also an O365 account on the same tenant of the secretary, what's the idea to create a script/rule/an application in Outlook to mirror what's in his primary Calendar to the 2nd one?