No.
PayVeX is specifically designed to be easy to sell files, we don't want someone to abandon their cart or have to keep track of login information. For this reason, when someone buys a file, they are able to download it as soon as payment is made.
If you're concerned about transaction fees, I suggest using pecunix.
PayVeX is all about making it easy to sell digital goods, having to step through an "add to cart" then "account creation" and finally "checkout" will result in lost sales as people abandon the process part of the way through.
We're trying to avoid that problem.
We at geniegate.com also offer a Membership Management Package that currently works with paypal. It would make more sense to modify it for digital shopping cart use than to add a cart to payvex.