While I have no suggestions, I do have a question or two:
1. Wouldn't the unique login/password equal roughly 1k in size?
2. If so, wouldn't that only take up approximately 10 megs of space? That doesn't seem too overly large to me. What is your max allowable database size?
3. Are these cd's that you are burning yourself or are they being pressed at a manufaturing plant? If so, each of them should have a unique identification number on them. You could use those numbers to verify that the person owns the cd (or at least has access to it).
This is indeed a unique and interesting question. Now you have me thinking (that rarely is a good thing, according to my wife).