Hi there from the Netherlands!
Old topic, but I just wanted to let you know that retrofitting a CC is possible on the E89.
I have an 2010 Z4 sDrive35is with nearly all options, except CC. In the Netherlands this model is not even sold without CC, but I imported mine from Germany.
Anyway. You need to replace the full set of steering column handles with the one that has a CC and of course you need a new cover because of the additional hole
It cost me about 400 dollar for the set of handles, 50 dollar for the cover and coding took 2 hours at a BMW specialist. Which parts you need exactly depends on the options you have, e.g. heated stearing wheel, rain sensor etc. Find the parts you need on realoem.com.
Stories are told that you need to replace the tacho (around 800 dollars here
). You will only need the tacho for the cruise control indicator led around the speedometer. If you have a tacho without this led, the CC still works but only displays in the small screen in the middle.
Once coded, you will have CC with brakefunction, hope this helps
Pics:
Steering wheel off:
Old and new handles next to each other:
Fitted:
Coding: