Discount for purchase several products in MarketPress

Hi there,

I have a product group with several variations, and here we want a discount if the customer order 5 products or more from that group.

My problem is, that if I use a coupon code it covers whatever the customer buys - and this is not the intention. Next I had an idea of making a variation within the group with a negative amount, but this isn't possible.

Anyone knows how to do it ?

rgds
Leo