You can set default values for cloned fields by assigning an array of values to std parameter.
Assuming you have a cloned text field phones which store phone numbers. You can set default value like this:
$default = array(
'0123-456-789',
'001-002-003',
);
// Then in your field
array(
'name' => 'Phone numbers',
'id' => 'phones',
'type' => 'text',
'clone' => true,
'std' => $default,
)
