Help required in building an automatic download after Paypal payments

I want to make a script so that when someone has purchased anything from my paypal account, then after payments, he automatically gets forwarded to the respective page. on a web page to get the direct download link.

I know Paypal provides a success URL option, but I don’t want to use that as that will be available for all.

Can you guys please give me idea of doing this.

I’ve used LinkLok to do this, and it’s great. Otherwise, go for a hosted solution like eJunkie or FastSpring.