I think you may be refering to bending the note Don.
This is best done on a diatonic. (BTW I think "smooth growl" is a perfect descriptive phrase)
An excercise that may help.
1)Draw in from hole 2 as you would usually.
2)As you do pull your tongue back & against the bottom your jaw
if you draw hard enough you should hear the note go down in pitch ("Bend")
3)Try tightening up your lips & jaw or whatever helps to get the air column down to the lower part of your mouth.
Does this help?
I will post on how this relates to cross harp later.
Promise: )