Advance Pricing - Quantity break based on Item Group

Hi,

I need to setup Advance pricing based on following rule:

Quantity based discount on price is to be offered on items belonging to a item group. (Example any item belonging to a price group say Q1  is ordered along with items from same group  and the combined quantity of these items belonging to a same group exceeds a threshold of say 10 Quantities then the discount need to be applied on each of these items belonging to same group). Basically Quantity level threshold is not for a single item but summation of quantities of all items belonging to a same item group.