It’s not a new idea but karaoke is still is very popular.  You can hire a professional karaoke unit or simply download an app and stream the video and music to your home TV.   Get a bit of practice on how to use before the big night.

Ideally you want to be able to control the musical key so as to allow for different voices and tempo adjustment is important.  Also look for apps that allow the recorded singer to be played at full volume, low volume and silent as some people will feel more confident if they can hear the original voice as they sing along.  Some of the better apps allow you adjust the singers tone ie: raise or lower just to help make them a little better in tune.   However adding reverb ( slight echo ) will help cover a lot of sins.  This site offers advice on best Karaoke apps http://bit.ly/2pwKMF3

A video camera is mandatory in order to keep the evidence for future extortion 😉