If you don't have a PayPal card, you have to use your PayPal balance to buy an Amazon Gift Card from a third-party site (like eGifter or Dundle). It adds a 5-minute chore to every purchase.
Here is a review of the experience based on the common workarounds: The Good: Flexibility and Security buy from amazon using paypal
You can still earn PayPal rewards points on these purchases if you're using their branded cards. The Bad: The "Gift Card" Tax If you don't have a PayPal card, you