Easy Enough - Have a space on the ballot Marked "None of the Above" - If on the count the None... Ballot wins you re run the election 4 weeks later - but none of the previous candidates can stand.
If its a mulity seat ward then those candidates falling below the "None... " ballot are eliminated, and a second round follows for the still vacant seat.
Three candidates to be elected
R Goodway 2000 votes Elected.
None of.... 1800 votes Eliminating level
A Whittall 1700 Votes Elininated