It should be possible using a magic switch. Add a line to the Elevator+ mixer with a fixed value input, which will then act as an offset, and than make this active on MS2,3 or 4. Then in the chosen magicswitch select the airspeed at which you want the elevator deflection to come on and go off, I would recommend adding a 2nd switch so you can make this action switchable. You can also use the same magicswitch to start the speed readouts in the sensor menu as well, so as well as the elevator deflection you'll get a verbal speed readout.
