You've even created a new category: the supervisor of the ethical wall. It sounds like something out of The Wizard of Oz. It's really odd.
One of the chief functions, as I understand it--I've never been in the PMO--of the chief of staff to the Prime Minister is to deal with a lot of inquiries from the chiefs of staff for ministers, to be a go-to guy. You won't be able to take meetings with most ministers, and you'll have to assign your deputy chief of staff to take those meetings.
Isn't it true that your deputy, under your direction, will be undertaking a lot of the work that would normally be done by the chief of staff? And if that deputy is under your direction or control, how are you completely arm's length from the issue?