Your best bet is to perhaps get a status match to a *A programme using your AF/KL Gold status. Go to the BD forum, and you can see that BD will status match your Gold Status to their Gold Status.

Once you are BD Gold which is Star Alliance Gold, you will be able to take an extra 20kg luggage on all Star Alliance flights which will include the LH flight.

But it will depend on how fast BD will status match you. You might be able to send them a fax etc. Go to BD forum for instructions on what to do.

Alternatively, you might want to get an award ticket on AY or BA from FRA to GOT. Then you'd get 30kg per person.