I don't see why it could not be added in. Couple of things to note; mine is on the same circuit as the electric water heater element and there is a cut out solenoid to keep you from running both at once and overloading the circuit. You have a limited amount of power to use so you have to manage it properly.
The fireplaces are fairly shallow 8"-10" so you have a fair bit of wasted space behind them if you install them in place of a regular cabinet. They are held in with 4-6 screws and then plugged into an outlet. Rocket science it ain't.
Aaron