Or they get really smart and not fight over Thrace at all?
So the Bulgarians have Dobruja and the Black Sea coast to Constantinople, the Greeks have Thrace to Constantinople, the Serbs and Bulgarians split Macdonia, and Constantinople (and the Sea of Marmara islands) is independent. You have four sets of coastal artillary controlling the Straits, which Russia won't like at all, but will please Britain no end.
You note that I am calling it Constantinople. The people are really the refugees from ethnic cleansing in the rest of the Ottoman Empire and the parts just conquered. Maybe an independent commission to administer under a figurehead American who decides that Constantinople is a country and lets what is supposed to be a fake front legislature take power?
Maybe he controls the legislature by a regulation that when the legislature is dissolved, the old legislators have to wait out the next term before the can run again? Kind of puts a spike in demogogues if somebody else gets the benefit of the new election. Have secret votes on the dissolution and the guys in power will disregard any instructions about having an immediate new election, or maybe the term limit is a year?
So the different ethnic groups learn to get along with each other and make money instead of war, a Switzerland in the sun.