IS Retail: Vendor Rebate based on Retail POS Sales

We are a Retailer with vendor rebate agreements. We run SAP IS-Retail on ECC 5.0. Some vendor rebate agreements are based on purchase volume, some are based on POS sales volume. We have been successful configuring the purchase-based vendor rebates.

However, we're having some difficulty determining how to set up the sales-based vendor rebate agreements. Has anyone done this successfully? Can you summarize the steps?

Thanks,