It almost sounds like you could do it with e-junkie, by making a .pdf of the certificate and then using the cart to deliver. But I am not sure. Also, you would not be able to get the recipients name into the certificate that way -so it would look the same to everyone.
I don't know. But I like the idea, and it sounds like something that would work for a lot of service businesses. I bet if you keep looking, you will find something.