Came across this 'trick' in a youtube video, but it has been working great for me. All she said to do is to relax the tongue, chatter stops. That's it. The non-stop inner dialog is like preparation for talking, so keeping the tongue from moving just stops it cold. She has some more ideas I'm trying about giving the brain something to do along with instructions, but the tongue trick is just so easy.
This is her description, at about the 44 minute mark
