I'm surprised that this is still offered. I registered and got the miles years ago. Good that you flag it, though. Another 500 miles opportunity would come for signing up for the electronic newsletter at Miles & More. Again, I did this over a decade ago, when the process was more obvious, so I'm not sure what the procedure would be now.
And don't forget to check out this thread periodically, although it has become rather cluttered with discussion about personalized offers and targets:
http://www.flyertalk.com/forum/lufth...tions-172.html