The rules say the person has a choice whether or not to open the present. I really don't think that the person will risk switching sides to gain an extra vote, especially if they are evil. If they are innocent and secretly wish to be evil then they might, but let's hope not. I don't see why you cannot tell us their name and establish credibility for yourself in case Rudolph doesn't buy your story. Also if they deny getting the present then u will know they are evil, though some may not believe you then. For myself, in absence of other information I will assume u are telling the truth.
Plant Ok your pulling it outta me but it went to you. I will be watching your actions very closely and i hope that you reallize that the town will be watching you.