I'm in UK and setting up a PHP website selling physical products. I will initially use Paypal standard integration. I have a bespoke cart already setup and I get customer's address on my website so that I can include a shipping cost to the order before transferring the cart data over to Paypal. Getting the shipping address on my site is ok but how do I then transfer that to Paypal without the user needing to re-enter it or changing it afterwards ?