During each night the Medium has access to a second secret channel, where they can ask a question, once day starts the channel is locked, and a Yes/No poll is created.
All dead participants are able to vote on it during the day. Of course, there can be members of all teams in the dead participants.
The question needs to be one simple yes/no question without any hidden meaning to it. Not voting as a dead participant should not give the Medium any information.
Once the day ends, the poll is closed, and the Medium gains access to the second secret channel again.