That's a good point. I don't think the creationists would agree to such an arrangement, because they can only lose or break even: if he wins the debate, people will say "Great, he can out-argue some random college student, so what?"; if he loses, people will say "Hah! He can't even win a debate with some random college student!" There would seem to be very little incentive for a prominent creationist to submit to that.