One technique used a lot in the old pre-aftertouch days of synths, was to use the middle finger of your left hand to bend the pitch up and the index finger to give the modulation wheel a small lift whilst lowering the pitch wheel back to its detent position. This gave a nice subtle vibrato to the otherwise rather static sounds of old monophonic synths.
In those days I can remember using elbows, nose or any free appendage to get some more controlled variation into the flat sounds. Thanks God for technological advances such as SA, huh?