Custom thank you page for a specific product

I am using a the Simple PayPal shopping cart which is great for my needs. However, I would like to add a custom class to one product which would go to a different thank you page from the default that every one else goes to.

The reason being is that I want the buyer to fill in a short form to provide extra information. I don’t want that information to go on the PayPal form.

Is there a way I can add a class to this particular product button so that after successful payment it redirects to this custom thanks page?

Thanks for your help.