• Create a GPG / PGP key and put the private half of the key on a USB drive that you give to someone else.
• Have your program encrypt the master list with the public key and save that to a separate USB drive.
• After your window recover the private key and decrypt the master list.

Alternately you could look at some sort of secret sharing implementation where you encrypt and split up the master list into n chunks that you need any m of them to recover the original master list. Everyone gets a chunk of the list with their assignment and you'd have to have m of them collude to get it back (so you'd want to set m sufficiently high, of course).

(Well, you did say you were over-engineering . . . :)