Discounts from vendors on purchase orders

I am using Quickbooks Premier 2004. I purchase inventory from a vendor that offers a 25% discount for certain items if you purchase more than 6 in an order. A typical invoice will list all qualifying items first (at their normal prices) followed by one line listing the total for all above items before the discount is applied. The next line is a negative amount subtracting the 25% discount for all above items. Any items not qualifying for a discount are then listed at normal price on the invoice. I cannot find a way to reflect this discount when receiving items in Quickbooks without manually calculating the discount on each item and overriding the cost from the original purchase order. I tried to create a discount item and use it on the purchase order the way you do on a sales receipt, but it just put the total discount into a discount account, left my COGS at the normal prices and resulted in bad data for COGS and gross margin in the Sales by Item report. Is there a better Quickbooks product that would allow me to enter two costs for an item in inventory or solve this problem without so many manual calculations? Thanks!