Paypal to Calculate Shipping

Hi there, I'd like my cart set up so that the only way to calculate shipping costs is via Paypal when you go to their payment page but the only way I can figure out how to do this is to set the cart to Free Shipping. The problem with that is that it's misleading because Paypal will actually charge them shipping based on their zipcode when you transfer to their payment gateway. Any suggestions?

Thanks.

Check out my explanation (and some possible downsides) here:

http://forum.opencart.com/viewtopic.php?f=10&t=30413

thank you!