I believe you are confusing things. You want to bank the miles from the LH flight into your US Airways account so you must go through US Airways to obtain credit. Going through LH for retroactive credit means you'd be adding the miles to a LH Miles & More balance.

Go here: https://membership.usairways.com/en-...e/default.html

At the bottom is how to claim missing miles credit for partner flights. Note that at the very bottom the footnote indicates which airlines require the boarding passes to get credit. From my experience, US has always wanted the boarding pass for a flight regardless of which partner airline I was claiming.

Major rule of thumb if you don't already follow: Always, always, always retain your boarding pass until the flight segments are credited where you want them.