Hello Matt
I was also searching similar thing to give the trial quiz to guest user.
But as moodle does no allow quiz module for Guest we have created our own code to create a random user and redirecting to the course quiz page.
Disadvantage of this code is that for each quiz attempt a new dummy user is created.
Ashish,
EddyTools (TM)
Anwesha Software Solutions Pvt. Ltd
http://www.eddytools.com