I want to retrofit heated seats into my E70 X5 and I only want a 100% OEM looking solution.

Coming from the e46 / e39 / e9x school of thought I thought this shouldn't be too much trouble but alas there's no heated seat retrofit kit available from BMW for the e70.

However, I'm sure it is possible. In fact I know it is because the nice people in Cartronics.co.uk said they could do it but quoted about 2,500 which is bit steep for toasty buns.

I've done a bit of research so far but have not yet found a how to guide. I've also spent time on bmwfans.info looking at parts diagrams for E70 X5s with factory heated seats and without but there does not seem to be a difference in seat part numbers between them, nor are there clearly identifiable parts for heated seat pads.

I figure there are a number of separate parts to the solution to this problem and it's the heated pads that has me stumped.

1. The buttons - that's solved. I just need to replace the heating controls for a unit with the heated seat buttons like this one

2. Wiring - If the loom required isn't there then it'll be a matter of retrofitting it / running the required wires. This isn't a huge issue.

4. Coding - the heated seat option needs to be added to the build. Again this is not a big issue

5. The heat pads - here's my problem. I don't really want to go buy 2nd heated seats as my seats only have 23k miles on them and replacements seem pretty pricey on ebay. I'm wondering are heated seat pads available for the e70? How are they incorporated into the seats on cars with heated seats from the factory? These must go on the blink from time to time and can't require a new seat to fix every time.
Alternatively, would the retrofit heat pads from an e9x work?

If anyone has any ideas on how I might do this please let me know, there's plenty of smart folks on here so someone must be able to work it out.