After some years of intensive use, I'm not aware of such an option. Instead of setting amount to zero, you can also set the destination to none, but also for that there is no shortcut. There is a shortcut to set the destination: press LFO-button and turn relevant knob. You could in this way choose a destination which has currently no influence on the sound. For example, if you disabled the effects anyways, you can use that shortcut to assign the LFO to the effect amount (thus, holding LFO button and turning effect amount), thereby effectively disengaging the LFO.