Half leather are rare as rocking horse poo. To wire in heated seats you need to take out the seats and the centre console (incl radio, air con - which needs to have the heated seat controls on them), gear gaitor, armrest etc. Then the wire needs to be wired and run along the centre console, then under the carpet to the gap under the seats where the other wiring harnesses are. That bit was a ****** nightmare... I helped a mate do it last weekend!
There's a thread somewhere on here where someone retrofitted them. Very good and detailed write-up with pictures, but I can't find it at the moment!