A little out of the box thinking (assuming that's what you're looking for), but you can assign the mic input to two channels in SAC, and put the signal switch on the second channel. Then put a levelizer on the first channel, keyed to the second channel's signal, with a reverse gate. Turn on the signal switch, and when you get audio on channel 2, channel 1 gates and turns off. This way the signal switch essentially bounces the audio between channel 1 and channel 2. I've done some odd things with the levelizer...