How to give out a limited number of gift card codes?

I'm distributing a survey and want to give out gift card codes to my participants. However, I only want to give out a limited number of codes and I cannot give the same code to more than one person. Is there any way to dynamically assign codes each time a user completes me survey? I've tried using a "quota count" to authenticate a user into the survey and give the code from there, but I realized that quotas are only incremented when a survey session completes, so this could end up with two people getting the same code!