Add similar field like "Additional Shipping Costs (for individual item)" but excluding item 1

[Vanlombardi]

Hey guys,

Actually i've set my shipping costs with the weight trick.

So I need to add another custom field (or modify existing one) for an item I want to add X€ to shipping costs for each additional item (ONLY THIS INDIVIDUAL ITEM) in the cart.

 

Because when I add this item to the cart, shipping does: "x€ from carrier weight rule + y€ from Additional Shipping Cost". I need this to be "y€" when only 1 item of this product is bought, and add "x€" for each additional item.  

 

Anyone achieved this? Any ideas?

Thank you very much!