Joomla affiliate program (through paypal)

We have a site built with joomla and we need an affiliate program developed for it. We don't have a cart system and use paypal links exclusively, so all we need is a way to set a cookie and then pass the affiliate ID through to the paypal system so it shows up in paypal notifications to the vendor. The system will need to: - set 90-day cookies based on unique affiliate id - set cookies on any page using a GET variable (url?a=<affiliateid>) - embed the affiliate id into the paypal links in such a way that the vendor will see it when the paypal notification email comes through It should be as efficient as possible so that changes made to the program later are easy to arrange, and that paypal links created by the vendor later will also contain necessary code to embed the affiliate id.