I edited my comment. I misread your question. This is the hypothetical solution. Let's say there are 1000 voters. You premine 1000 coins then send it to each v

I edited my comment. I misread your question. This is the hypothetical solution. Let's say there are 1000 voters. You premine 1000 coins then send it to each voter. Voter then can vote with 1 coin. So you can make sure the voting process is valid, and you can hide the sender in the smart contract. Of course, the technicality is not this simple. But you get the idea.