Discount for group of products

[Bravos]

Example

I have t-shirt - different colors and sizes

The shopper wants to buy 10 t-shirts S-size white color, and 10 t-shirts M-size black color

But the t-shirt - is the same product

Question: how can i make one discount for this? i mean summ discount for this combination
Not for every 10 of them, but total for 20 t-shirts

Need it very much

Please help

joom: 1.7
vm: 2.0.4

[Bravos]

anyone?
f////@#$%#

[jenkinhill]

Maybe use http://extensions.virtuemart.net/extensions-virtuemart-2/quantity-related-calculation-detail