Datamapper set_join_field without update

Question

I'm trying to save some date with a join_field basically I have an add-up function and an count-down function

if(isset($_POST['min_product']))
        {
            foreach($_POST['min_product'] as $index => $min_product_id) 
            {
                $minproduct = new Product($min_product_id);
                $minproduct->save($order);
                $minproduct->set_join_field($order, 'amount', $_POST['min_prod_amount'][$index]);
                $minproduct->check_last_query();

            }
        }

if(isset($_POST['product']))
        {
            foreach($_POST['product'] as $index => $product_id) 
            {
                $product = new Product($product_id);
                $product->save($order);
                $product->set_join_field($order, 'amount', $_POST['prod_amount'][$index]);
                $product->check_last_query();
            }
        }
        $this->set_order_row($order->id);

the Query's look like this:

UPDATE `link_orders_products` SET `amount` = '-1' WHERE `product_id` =  2 AND `order_id` =  391
UPDATE `link_orders_products` SET `amount` = '5' WHERE `product_id` =  1 AND `order_id` =  391
UPDATE `link_orders_products` SET `amount` = '1' WHERE `product_id` =  2 AND `order_id` =  391

As query i would like to have something like:

INSERT `link_orders_products` SET `amount` = '-1' WHERE `product_id` =  2 AND `order_id` =  391
INSERT `link_orders_products` SET `amount` = '5' WHERE `product_id` =  1 AND `order_id` =  391
INSERT `link_orders_products` SET `amount` = '1' WHERE `product_id` =  2 AND `order_id` =  391

The problem is that the amount of the first query will be override by the amount of the last one. But I would like to have them all tree in to inset in my database

My question is How do I insert the value's that are handled by the set_join_field so they don't update?