In the ES/IV, the side stick controls are all push/pull tube linkages. 

 

See picture below: 

 

The black weldment is the stick mechanism.  The “sick” is jutting out of the upper right corner of the photo.

 

The horizontal green tube goes down the side of the fuselage and eventually back to the elevator – for/aft movement moves the elevator.  The two sides (pilot/co-pilot) are joined behind the back seat.  – nothing real special – just several tubes, rod-ends, and a few bell cranks.

 

The vertical silver tube goes down to a bellcrank and out the wing to the aileron – side/side rotational movement moves the ailerons.  On the ES, the two sides are joined under the front seat.  On the IV the two sides are joined by an additional linkage under/behind the instrument panel.

 

On the pressurized versions the rods all go through a bushing where they exit the fuselage pressure cavity.

 

One drawback to the design/arrangement is that is consumes approximately 3” of useable space(width) on each side inside the cockpit (under the arm rest).

 

 

 

Can’t comment on the retro-fitting required for a Legacy.  Seems like it would be a lot of custom linkage either behind/under the panel (where a Legacy has limited room) and/or behind the seat – along with a loss of interior width.