If you wait long enough someone will offer to rent you their teenage kid as
an observer (if you don't have any bribable ones of your own).
Gertrude
I'm sure the above is a light hearted comment but it does seem to suggest
that the requirement is not that important and any passenger enjoying the
view would suffice.
The requirement is not for an "observer" it is for a "competent observer" - which
I would take to mean someone who understands they are performing a safety
function, knows how to Look Out and knows what needs to be reported,
when and how, to the "eyes down" PIC.