Just simply zero every even or odd sample, with some simple ramp when it turns on or off to prevent 'clicks'.
Superpowered doesn't really offer a function for such tiny task. You can do it with the SuperpoweredStereoMixer, but it may be too complex for this simple job.
Here is code snippet 
bool Tempo::process(short int *output, unsigned int numberOfSamples) {
    bool silence = !playerA->process(stereoBuffer, false, numberOfSamples, volA);
    echo->process(stereoBuffer, stereoBuffer, numberOfSamples);
    reverb->process(stereoBuffer, stereoBuffer, numberOfSamples);
    float *mixerInputs[4] = {stereoBuffer, NULL, NULL, NULL};
    float *mixerOutputs[2] = {stereoBuffer, NULL};
    float mixerInputLevels[8] = {1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f};
    float mixerOutputLevels[2] = {left, right};
    mixer->process(mixerInputs, mixerOutputs, mixerInputLevels, mixerOutputLevels, NULL, NULL,
                   numberOfSamples);
    if (!silence) {
        SuperpoweredFloatToShortInt(mixerOutputs[0], output, numberOfSamples);
    }
    return !silence;
}