I am guessing you want to use that with the WP eStore plugin? If yes then note that the WP eStore plugin already uses the IPN (instant payment notification) feature of PayPal to do the post payment processing stuff (eg. deliver the digital products). PayPal only sends IPN to one script so if you add that bit of code it will send the IPN to the JROX Jam affiliate software instead of the eStore plugin and the WP eStore won’t be able to do any post payment processing work.
If they have an integration option like the iDev Affiliate software whereby you can call a PHP function for the commission award then I can accommodate that.