If the midikeyboard has two pedals, they can be used to change note legth thus freeing both hands. Initial notes length is set in menu of mscore. Then press and release of the right pedal = increase note length by 1, press and release of the left pedal = decrease note length by 1. Press right pedal and while holding it, you can press and release left pedal with each such action increasing note length by 1 to as large length as supported. Press left pedal and while holding it, you can press and release right pedal with each such action decreasing note length by 1 to as short length as supported. But it will take much efforts for feet. An easier solution is to press the key on keyboard and while holding it pressed, you can press and release right pedal to increase note lengths, left pedal to decrease. Could be already implemented, not checked yet.