I am with Beagle on this one.
My advice in such situations is for the student to always think of what they would do in a similar situation after they have their PPL.
The answer is either - a) Don't put the map (or anything else required in flight) there in the first place; or
Get the passenger in the right seat to do the searching while you fly the aircraft. i.e. ask the instructor in this case to retreive the map.
If the instructor refuses (very bad on their part), then simply say "You have control".
Regards,
DFC