Just to reiterate.
You must book an LH flight with the LH flight number (not a UA code share flight number).
You must book in Y, B, M or H.
You must have a paper mileage cert from UA.
You must call UA international reservations once a week and ask them to send a message to LH requesting the upgrade, because LH does not maintain a waitlist.
During the last week before the flight, you must make this call to UA every day.
You must not expect the upgrade to clear until a day or two before the flight.