I have a product and we are running a campaign for it to allow users to download a trial version. My questions is there any way to detect multiple downloads from the same computer but behind a proxy.

For example if a person uses a proxy server, changes his/her ip and downloads our trial version multiple times from different Ip's, is there a way to detect that it is the same person who's downloading the s/w. We use only Name and Email addresses to be entered before downloading our s/w and that can easily be created. We cannot add any other fields to the form (like phoneno.)