If I understand some of the 'hidden tips & tricks' posts I've found, All V8 X5's built after 2001 have seats with heating elements built into them, and the only thing I'd need to replace in my X5 would be the switch bezel in the center console.
Part Number 61318373740 at ~$190 list?
Or Part Number 61316949441 at ~$580 list?

Also, rear heated seats? What parts needed for retrofit? Should all have heating elements already, right?

Erik