E-junkie provides shopping cart and digital delivery technology. We work with payment processors like PayPal, Google Checkout and none of those support split payments.
However, if you create an affiliate program for your product and your developer can become an affiliate. Then, rather than selling via your direct link, use the affiliate link your developer gets after signing up for your affiliate program.
At the end of the month, E-junkie will provide you a paypal mass payment file using which you can pay your developer easily.