I modeled 'Mimmi' years ago before the decal set came out - I sprayed the fuselage gloss white and the determined the size of the squares running the horizonal length if the center of the fuselage side. I used a Microscale sheet of black decal paper and cut each square out and moved it into position. The black decal is thin enough that if the square was too short I merely overlapped another piece of decal to get it right. The squares on the top and bottom of this center strip were then reduced in size to match the photos. It wasn't all that tedious as it may seem.
Here's a url to Mimmi (and a couple of others).
Charlie Duckworth : Central Powers Aircraft Model Images