Quick ableton mapping question

i think most of you have seen moldovers vids. i want to be able to chop up sounds with the mute key . the way he dose it is, when the key is pressed down the track is unmuted and when the key is released the track is muted again. this is all when the volume fader is down but when the fader is up then the track plays normally.

so i have tried to make a black key on my midi keyboard do this except 1# i am a total noob at ableton 2# i cant figure out how to make it a hold command like in traktor, it is always a toggle.

thanks
drumer.boy