Add a click track to an existing recording

I have some backing tracks which are to be used for a stage musical production. They are difficult to follow as they have “Dramatic” pauses. I would like to add a click track to help the singer get used to the tempo. BUT Is there any way of synchronising a click track to an existing track. Or can one stretch the click track to match the audio?

If the backing tracks are not in “strict tempo” it is very tricky (time consuming) to make a click track that synchronises accurately with it as you will need to do numerous small adjustments to make it match fluctuations in the music. It is unlikely to be worth the trouble as your singer will probably find it as hard, if not harder, to sing to an irregular click track as to sing along to the original recording.

It’s probably easier to just tap on a mic in time with the music than figure out a way to get a synced click track.