Quick Export : add product post meta

// functions.php

function custom_product_meta($array)
{
    $array[] = '_length';
    $array[] = '_width';
    $array[] = '_height';

    //also works for size or color attributes, or data added by a plugin... to find the right key you need :
    //please refer to : http://codecanyon.net/item/woocommerce-quick-export-plugin/6040506/faqs/20773

    return $array;
}
add_filter('wqep_included_order_product_keys_filter', 'custom_product_meta');