The problem is how he could be able to control the country when the Baltic Germans are about 8% of the population. Of course the German army could prop it, but after they withdraw, what would be able to stop the Latvians and Estonians from overthrowing it? The Baltic Germans would need to control Courland and Estland as well, or Livonia would be quickly divided between the two. And if the Baltic Germans manage to keep control by force, Communism would become very popular in the Baltic states...
I was thinking something like this: After taking Latvia an Estonia in 1917, Germany takes more effort to form an actual administration there, using not only Reichgermans and Baltic Germans, but the local population as well, forming a United Baltic Dutchy similarly how the Kingdoms of Lithuania and Poland were formed. After the armistice, the Germans withdraw, but the local administration stays in place, only the personel is replaced, so the UBD lives on, only as republic rather than a monarchy. Germany also maintains an army there, only not as the Ober-Ost, but the "UBD Army", kind of like the German remnants in the Ukraine or the Saxon volunteers in Lithuania. Both Estonia and Courland (Latvia) secede from it, but the remaining part (Livonia) keeps the two states out thanks to its slight military advantage. Before they manage to get ready to take it out, possibly with French reinforcements, the Soviets invade; the three states put their differences aside for the time of the war, and Livonia keeps it going even
after Estonia and Courland-Latvia sign a peace treaty with Russia. Livonia becomes the shelter for Russian Whites under Yudenich and the Bermontians, giving it a stronger negotiation position in Paris than either Courland and Estonia, thus allowing it to retain independence after the end of the hostilities (Poland and Finland require all the help they can get and don't have a problem with Livonia, so they might beg France to let it be).
Livonia is messed up internally of course and has all of its neighbors hostile to it, but this would still fullfil the OP request even if it was to crumble in 1924, wouldn't it?
