gistfile1.php

$this->map = new MigrateSQLMap($this->machineName,
  array(
    'sku' => array(
      'type' => 'varchar',
      'length' => 32,
      'not null' => TRUE,
    ),
    'delta' => array(
      'type' = 'int',
      'unsigned' => TRUE,
      'not null' => TRUE,
      'description' => 'Type of ticket',
    ),
  ),
  MigrateDestinationEntityAPI::getKeySchema('commerce_product')
);

...

public function prepareRow($row) {
  ...
  $row->delta = 0;
  ...
}

...

public function prepare($entity, stdClass $row) {
  for ($delta = 1; $delta <= 7, $delta++) {
    $variant = entity_create('commerce_product', array(
      'sku' => $row->wathever,
      ...
      'property' => $row->foo,
      ...
    ));
    
    commerce_product_save($variant);
    
    $source = clone $row;
    $source->delta = $delta;
    
    $this->map->saveIDMapping($source, array($variant->sku));
  }
}