You can solve that simply by putting all such votes inside signed envelopes, and waiting to count the contents until all the envelopes can be checked for duplicate voter details. In Australia this can be forced on you if you are caught double voting, or you can opt into it if you don't want to appear on the (public) electoral roll (and hence can't be ticked off), or you're voting from outside your electorate (so they don't have a copy of your electorate's roll).