Line discounts

Hi, I would like to be able to set up particular customer with brand discounts. So say, for example:

We have items from brands A, B, C and D

Brand A contains 5000 individual items

Customer X should receive 10% off brand A

So is there a way to set that up for customer X, or does it have to be 5000 individual line discounts set up in sales lines?

Thanks for any help!