Instead of counting the votes cast, draw one at random. That candidate is elected. The more votes a candidate receives, the greater the probability of them being elected.
At a constituency level, this is very unfair to the individual politicians, particularly those who don't get elected despite being the most popular. However on a national scale across all the different constituencies, the law of large numbers means the net result will tend towards one that closely represents the will of the people.
There are no wasted votes and no motivation for tactical votes. Every vote has just as much chance as any other, no matter where you live. At the moment, how much your vote matters is a postcode lottery, because First Past The Post creates safe seats where voters have no chance of determining the outcome of the election. Switching to a raffle system would move the unfair lottery element away from the electorate and onto the politicians themselves.
Of course politicians would hate this system, as it would be unfair to them, so it will never happen. However the FPTP-supporting politician should question why they are happy to make the system a postcode lottery for the electorate, but not a lottery for themselves.
The only way of running elections which is fair to both politicians and the electorate is multi-member constituencies.