Account holder's address not picked up by PayPal when cart is virtual

ZC v1.3.9f (PPEC Sandbox): An account-holder logs in, places a virtual item in their cart, and goes through the checkout steps choosing PayPal as the payment method (payment->confirmation->PayPal), when they get to the PayPal payment page ... they have to enter their billing address as well as payment method!

This appears to be tied to the fact that the shipping address fields are not sent to PayPal when the cart is "virtual"; if the customer returns to my store, adds a shippable product to their cart and then returns to the PayPal process, the customer's address is shown by PayPal.

That's by design.

PayPal allows you to submit a *shipping* address. Not a *billing* address.