Sorry, but given the inexperience of the HP, the Captain should have had the guts to say no.
I was about to type something along the lines of 'easy for you to say', and then I carried on reading...
Whilst I was captain of a royal flight, HRH asked to sit in the left seat to which I declined and suggested that if HRH wanted to fly the aircraft I would over to arrange a 'Senior Officers Course' for him.
Fair dos.