At www.pointandsave.net we have a coupon generator that directs customers directly to PayPal after redeeming a coupon from our site with the amount due after the coupon value has been deducted. However, the only way I see that you could do that is to figure out how much of a discount you would have to give on each item so that by the time they purchased three it would equal half off the third one. Just put a limit on the purchase quantity. Hope this helps. If not atleast check out our site. Thanks.
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