most of us do know that, during the 19th century, the balkan territories of the Ottoman Empire would give in to various armed rebel groups of the ethnic-independentist type, leading to the creation (or re-creation) of various nations such as Bosnia, Serbia, Bulgaria, Macedonia, and Albania.
So, the challenge here is to breath some fortune to the Ottomans, allowing them to hold on for a few more territories like Albania, Macedonia, Southern and Eastern Bulgaria, and possibly (but more hardly) Bosnia and Northern Greece, either through tactical military victories or loyalty of some ethnic groups.