I was asked to make a helper program that copies participant list from a survey to another. I did basically

$people = $conn->list_participants($sessionKey, $survey_id_source, 0, 100000, false, array('attribute_1'));
foreach ($people as $person)
$conn->add_participants($sessionKey, $survey_id_destination, array($person), false);

and this works IF id numbers in the participants table of source survey are consecutive numbers. But if there is a gap I got participants that have no name nor email.