Hi,
The purpose of PayPal Express Checkout is to bypass your website checkout...
Here is a solution:
You deactivate the display of the PayPal Express Checkout button on the cart module and keep it activated on the checkout, but you move the cart view of the checkout workflow at the end of the checkout.
That way, the button to go to PayPal Express Checkout will only be visible once the user entered his address and selected his shipping method.
But then, if you do that, here is my question to you : Why do you use PayPal Express Checkout in the first place ? The PayPal Standard payment plugin will basically render the same purpose for you and will better be integrated to the payment methods selection interface.
As I said before, the goal of PayPal Express Checkout is to bypass your checkout, so configuring your website and the plugin for it to go through your checkout completely defeat the purpose of what PayPal tried to do with that payment gateway.