Cookies are built to be site specific. One site is not suppose to read the cookie of anther site.
The variable has to be on your site for you to pull it dynamically. Since the user is on PayPal when the variables appear, there's no way for you to grab them.
You could make 8 different confirmation page and change the code around on each one. I don't know if PayPal allows a different confirmation page per product - never tried that with PayPal before.
If you manage to make that work; would like to hear about it.