Using the PayPal button creator there is not a way to create a button without it taking your customer to the check out page. However, I am not sure if you are aware there is a link on the cart page that will take them back to the website to continue shopping. If this will not work for you, you may want to consider looking into a third party shopping cart. Here is the direct link to take a look at PayPal Certified Shopping Carts. I hope this helps.