WooCommerce CSV Exporter – How to access line items?

I use the Customer/Order CSV Export plugin from WooThemes to export orders from my shop. However I want to add additional data to the CSV output per line item (do some calculations etc.) and I found below information on the official WooThemes page.

However I want to access the line item data, how can I achieve this? For example: How can I get the ‘item_total’ which is not stored in the postmeta database (the postmeta database is listed in the example below) ?

Is the line_item data included in the $order_data? How can I access it?

function wc_csv_export_modify_row_data( $order_data, $order, $csv_generator ) {

    $custom_data = array(
        'column_1' => get_post_meta( $order->id, 'some_meta_key', true ),
        'column_2' => get_post_meta( $order->id, 'some_other_meta_key', true ),
        // add other row data here in the format column_key => data
    );

    $new_order_data = array();

    if ( isset( $csv_generator->order_format ) && ( 'default_one_row_per_item' == $csv_generator->order_format || 'legacy_one_row_per_item' == $csv_generator->order_format ) ) {

        foreach ( $order_data as $data ) {
            $new_order_data[] = array_merge( (array) $data, $custom_data );
        }

    } else {

        $new_order_data = array_merge( $order_data, $custom_data );
    }

    return $new_order_data;
}
add_filter( 'wc_customer_order_csv_export_order_row', 'wc_csv_export_modify_row_data', 10, 3 );