In addition to the keyboard commands,
  Shift-W - Full 
  w - Increase 
  s - Decrease 
  Shift S - Idle
allow the ability to map an analog axis to throttle for GVs.
Similarly to how the throttle currently works for Aircraft and is able to be assigned to an analog axis.
  Shift + - Full 
  = - Increase 
  - - Decrease 
  Shift _ - Idle