I want to say I read somewhere that the wiring and hookup for heated seats is there even if you don't have it.
It might be worth pulling the seat and looking for it. Like I said "I WANT TO SAY I READ IT SOMEWHERE" although I can't find it now.
If the wiring is there, it would be almost as simple as pulling the OEM heated seat pads out of a car, or even swapping in limited seats. The limited seat swap would be plug and play....IF THE WIRING IS THERE. Swap the console / switches and you'd have an OEM setup.
Otherwise, @
funwheeldrive is correct in seeing aftermarket heated seats. I've seen a couple FRS with that as a dealer installed option, may be worth looking in to.