If its really critical for you to develop a vibrato, then perhaps a vibrator IS the answer! Better yet, glue a variable speed sander on your ass and have at it!

BTW, vibrato on windblown instruments is done two ways. There is both a diaphragm vibrato (stmach vibrato) which is more in use among symphonic types and a lip/mouth vibrato used by most jazz players. On sax/clarinet for instance, the lip vibrato is done by retaining the same embouchure while forming the syllable "yah" in your mouth. This causes your lower jaw (and lip) to move up and down against the reed in a controlled manner. The speed is controlled by the yahs. Taken to the level of ridiculous, you wind up with Guy Lombardo's sax section.

Spaw