Discount based on total product quantity of the same category

[wallybz]

Hi,

with PS I can make a discount for a certain product category based on product quantity.

 

But the quantity is calculated per product:

 

For example I make a discount rule based on more than 20 quantity then apply 5% discount.

This rule works per product but not for the sum of more products of the same category.

 

I would like to apply the % discount based on the total sum of product of the same category.

 

Any idea on how to do this?

 

I googled and looked for a plugin but I didn't found any solution.

 

Thanks in advice