I was under the impression that if you have one that works, adding a second is user-doable. I don't recall the procedure, but I do remember seeing it somewhere, perhaps in the owner's guide?
Turn ignition to RUN or ACC. Momentarily jump pins in programming connector located In LR qtr panel area(taped to harness will have W/Y and GY/Y wires). All doors will lock then unlock to confirm programming mode. Press any button on 1st transmitter. Door locks will cycle to confirm programming. Press any button on 2nd transmitter (up to 4 transmitters total possible). Turn ignition to OFF. Locks will again cycle to indicate end of programming mode.