Give this a listen... Not bad for a MIDI controller!
A thumb button activates vibrato/pitch bend mode, where once the gate is active maps z axis acceleration to pitchbend. On top of that, when the keep is pressed, the instrument angle is stored, and a 5 degree dead band created. Any instrument angle inside this dead band just allows vibrato via acceleration, outside this dead band it activates the traditional pitch bend.
This allows one thumb key to gate vibrato while still having full pitch up/down control.