You can attach the files to your reply by uploading the zip archive that contains the files. When I tested this out I was able to login to PayPal and return to the confirm page with all of the value showing except for the shipping. Is this not the same result that you are getting currently? If you are getting a different result please post back with some screen shots so we have a reference for what you are seeing.
One of the problems with updating PowerStore to work with custom shipping charges is that the entire PowerStore was designed to work in it's default state and making updates to the site with eCart can have other effects on the site. This is why we do not support customizing the PowerStore.