Customised certificate security

Hi All,

I've added a customised certificate at the end of a quiz which can be printed off by the learner. However, I want to be sure that only the person that successfully completed the course can print off the certificate. There seems to be no way of stopping re-printing the certificate with a different name. i.e. one person takes the course, fills in his name in the field pop up box, prints off a certificate but then returns to the pass result slide and fills in somebody elses name and so on and so on until all his buddies have certificates too.

Does anyone have a quick, secure solution?