It is not really possible to redirect a browser to any URL without making that URL trivially discoverable. Even our download links aren't really hidden in any way that would be at all difficult to discover; they're just implemented in a way that's designed to prevent some popular anti-virus/security scanning software from trying to pre-fetch the link looking for potential threats, which would count as attempts made on the link and thus could prematurely expire the link before the buyer has a chance to claim their download.
You could set things up at your end so your URL is not directly visitable and can only be reached via redirection from e-junkie.com. Also, when we redirect to a custom URL, we append some order-specific data to the end of your URL in a query string, so you could have some custom scripting at your end which uses that data to verify the visitor as a paying customer:
http://www.e-junkie.com/ej/help.redirection.htm
If you'd need some help setting that up, we can recommend the competent, E-junkie-experienced developers listed in our directory here:
http://www.e-junkie.com/ej/developer-directory.htm
