Concerning your edit, not sure about other countries, but I can speak about the process in France.

We get (normally) ballots with the programs in the mail before the elections, so we can also bring ballots from there. Then the way it works when voting is

• there's a table with ballots from all lists that provided them (so missing the ones we're talking about here) and you can take any number of them
• then you go isolate in a cabin where you put the ballot you want, or nothing, inside an envelope
• finally your identity is verified, your vote is counted and you put your envelope in a transparent box

So there's not really a way to definitely know you're voting for an unlisted candidate here.