But each ballot is pre-filled out for a different candidate. The vote fixer already knows what's on all of your ballots, they just don't know which goes into which box. Photos showing what's on the ballot don't disclose any information. The attacker already knows that you have one ballot pre-filled for each candidate. The only secret is which ballot goes in which box.
You go into the voting booth, seal the N ballots in the N identical envelopes, being sure to keep track of where the ballot for your desired candidate is. You leave the voting booth and drop the one envelope in the vote box, and the N-1 envelopes in the discard box.
Even if you're forced to videotape inside the voting booth of your sealing the N ballots in the N identical envelopes, you could pull a quick 3-card-monty when leaving the voting booth. Even a quick random shuffle would be sufficient to statistically nullify your vote, or if you're only able to keep track of where the Dr. Evil ballot is, a quick deal from the bottom of the deck would guarantee a vote for a random opposition candidate. As long as there's some spot between the polling both and the ballot boxes that isn't covered by video, there's no way for a third party to know which ballot went where.
You aren't allowed to leave the polling station with any of the envelopes, and a tally of the ballots in the discard box will show what percentage of people have left the polling station with their discarded ballots. Any non-negligible percentage of "discard" ballots leaving the polling station will make the whole vote suspect. (The discard ballot count will also provide circumstantial evidence for which way the tampering is going, although Dr. Evil will always claim it's false flag vote tampering to make him look bad).
If someone is really coerced in sneaking their discard ballots out of the polling station, they could sneak N-1 ballots out and either put the ballot for Dr. Evil in the discard box or burn it right outside the polling station. They then show the jackbooted thugs the other N-1 ballots. They end up not voting, but at least Dr. Evil is denied the vote.
