Cover any suitable figures in chocolate and cream or, alternatively, field some model trees a la Black Forest. Then you can proudly announce you have Germans in the dessert.
Seriously if you want Germans in the desert post 1918, best to field them as explorers. The Treaty of Versailles put something of a crimp in large organised bands of armed Germans trekking into parts unknown. Of course now that they've finally paid off the war reparations.....