Most studdering plugins use "random" parameters to give crazy results. There are some good ones on the PC I am not sure about Mac. You will find most artists do them manually.. it is just about learning to edit. They are not that hard and you can make them just how you want them with edits.
Well.. Reaktor has a module that does something similar.. and Ableton Live has the Beat Repeater. I have not used Phatmatik Pro much and it is based on drums but you maybe can do some studdering with it on other things.
Someone needs to make the word "s t u t t e r" not be a face icon.
