You could allow access to that link about 5 times. After that, display a link that says something along the lines of "Thanks for using us. This link has been used 5 times already. If you wish to access it again, click here and we will send you an email with another authorization code (or whatever)". That way your users don't lose access to their stuff, and you can keep track of abuse. It's not a perfect solution, but it's better than nothing.