This may be actually impossible, but I'm filing a bug to discuss strategies for preventing mirrors of Wikipedia from including pages we NOINDEX. A good example of this is user pages or user talk pages, and the new Draft namespace on English Wikipedia.
Technically speaking these pages are free content just like anything else on Wikipedia (with the exception of fair use images, etc.). However, there are good reasons for us to not want content to be indexed by search engines and found by readers.
Numerous times, I've had Wikipedians bring up the valid point that mirrors erode our ability to control search indexing, because they mirror content we NOINDEX, but do not replicate the contents of our robots.txt.
There may practically be no way to prevent this. Even if that's the case, we should record why that is and WONTFIX this, as a point of reference.