Which sector is the non-international sector? (Iquitos is in Peru, Quito in Ecuador, so a Quito - Iquitos flight would be international as well).
You must mean flying LIM-IQT (there is no direct way on LAN to get to IQT from UIO).
LAN's website does not let you book "complex" itineraries. You could book two different tickets. Not sure if that would affect price.