Create external "Add to Cart" script out of php shop page

This very simple project contains the following mission. Today, visitors of our website have to click on a link to get to our gambio /xt commerce shop (PHP, CSS) when they are interested in a specific product. Then afterwards, they have to click again on a "add to cart" button. We wish to simplify this process. That means that our visitors shall be able to directly click on an external "add to cart" button. Therefore, a php script has to be extracted out of our shop that creates a new session, clears the shopping cart completely and adds the quantity "1" of one single defined product to the shopping cart. This project requires a PHP expert, but is quite simple at the same time. If you are interested, we will provide you further information. Regards Christo