Promotions : get x% off on 2nd product and y% off 3rd product.

Promotions : get x% off on 2nd product and y% off 3rd product.

Hi,

As the title says i'm trying to do a promotion for a product family called Franco. 

The promotion would be : get 10% off the 2nd franco and 15% off the third franco. Is that possible with the extension Special Promotions?

So to summarize, if you have 3 francos in the cart, first would be full price, second would be 10% and third would be 15% off. 

I can't seem to find a way to make a specific % applied to the second product and another % applied to the third only. 

I hope my question and the promotion i want to do is clear.
Thanks!