Good call. With the current release you'd need an Aux switch and an Expression pedal, or as you said, use two Aux switches to do that. HOWEVER, we recently anticipated that this was indeed cumbersome, so we've added an option to the Xnob (PLAYMODE) that let's you use the Play footswitch (middle one on TF) as direction toggle instead of a Play retrigger. That way you only need one extra switch or expression pedal mapping to do the half speed. We'll probably do another beta release with this new feature and some bug fixes shortly.