I never heard about a technique that I just thought of and tried out.
I was playing a line and let the last note ring out. I took my open palm over that note and fluttered it up and down to get a tremolo. This is analogous to what a harmonica player does with his hands. Sounds cool.
I couldn't find any references to this technique on the web. Tony mentioned that he knows about others that have done this and used their mouths going whaa whaa whaa over the note after you hit it.
I'd be interested about hearing more about this technique (using hand or mouth).