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Well that's really interesting and useful to me as I was about to look in to this for the car I'm buying and have extensive experience of this.
I've done this for my E93 M3 so don't be concerned but what you can do is buy the US mirror and buy a european mirror with the correct version of the homelink module.
There are a few designs of modules, but you want the one with the buttons at the bottom. Nearly all rear view mirrors are made by Gentex, and homelink is also a Gentex brand.
You can buy any european homelink mirror so long as the buttons are underneath the mirror. You then leaver the casing off (not hard once you know how) and switch the modules.
Euro homelink modules have circuitry front and back and an external aerial:
US do not.