Stereo to Mono ?

I have created a video with 3 audio tracks. Two voice audio tracks (in .wav files), and one stereo back ground track (in a .wav file).

Is there a kdenlive setting I can apply to have all 3 audio tracks mixed into an audio mono output [ie same sound on left and right] ? (as opposed to a stereo output).

There is a "Mono to stereo" effect, which really just copies one channel to another.