The only surefire way of getting some sort of incentive miles/points when buying from Amazon.com is this way:

Use a portal that gives you the incentive when you purchase from Giftcertificates.com

You can buy Amazon.com e-mailable gift certs from Giftcertificates.com which cost nothing other than their face value. E-Mail them to yourself or to someone else and then use them when purchasing from Amazon.com

The miles/points that you will earn from Giftcertificates.com do show up after the normal delay in posting to your account.

Good luck!