"Buy 2 Get 1 Free"

[andrabr]

The formula in the subject is very traditional and rather popular in its various incarnations. The general case is "Buy X items of the SAME product and get item X+1 with a discount of Y, no discount on item X+2".

I have looked at "better Together and Qty Discount mods and still cannot figure out a way to do this.

There is a horrible kludge of using many many levels of the standard Qty Discounts and back calculating the values for every quantity, but that sucks ***.

I have tried it for demo purposes: in the attached screen shot it's $10 for 1 item, but $16 for two, ($10+$6)+$10 for 3, and so on. Just look at the discount table and feel the pain.

Please do not ask me why I want it this way: I do not but I have to ?(a manufacturer wants to roll out a specific promotion ).

Help?