It basically requires a dealer to do the coding, but you may be able to get an independent who has the correct tooling. As it won't be a simple retrofit, I would tend to rely on the dealer. The instructions are fairly specific regarding upgrades to the latest software version prior to starting the job.

The Webasto heater is an expensive option, but it is an elegant solution. With the timer and remote control, you shouldn't have any trouble with the battery (at least not any more trouble than you may have anyway). If you want to do something a little simpler, and have access to mains power where you park, a stick-on silicone pad heater on the oil pan works well, at least to pre-warm the oil and thus shorten the warm-up cycle.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue