Perhaps an option would be to have the 1st Balkan War somehow spiral out of control into a larger conflict, bringing in Britain, France, and Russia on the sides of the Baltic states against the Ottoman Empire and her allies in Austria-Hungary and Germany?
Just a quip on the proposed PoD, since I discussed the scenario at some length sometime ago. A WWI spiraling out of the 1st Balkan War is quite doable.
However, it is bad news for the Entente, since it most likely involves Serbia getting its head swelled (more than usual, anyway) and refusing to quit when Austria and Italy warn it off Albania, perhaps because Russian diplomacy ITTL is experiencing a belligerant phase. Now, preventing Serbian expansion in the Western Balkans was one of the few issues on which Austrian and Italian strategic interests really aligned. Italy is totally going to stick with the Triple Alliance on this casus belli. Let's say that Serbia evades Austro-Italian ultimatum, both powers declare war, war expands to Germany, Russia, France, and Britain by an event chain much like OTL WWI. With German mediation, Italy and Turkey hastily bury the hatchet with a peace of compromise (most likely, Italy keeps Libya and returns Dodecaneso) and switch to being allies in the CPs coalition (Italy is promised Nice, Savoy, Corsica, Tunisia, and French Somaliland, Turkey is promised Cyprus, Aegean islands, gains in the Caucasus). Bulgaria most likely decides to backstab its temporary uneasy allies and long-time rival Serbia and lesser rival Greece and switches to the CPs like OTL. Romania sides with the Entente, hoping for gains from Austria and Bulgaria.
CPs: Germany, Austria-Hungary, Italy, Turkey, Bulgaria.
Entente: Britain, France, Russia, Serbia, Greece, Romania.
All from the start.
Serbia and Greece are encircled by the CPs and swiftly crushed, then the CPs armies turn and steamroll Romania. The Balkans are a CPs playground, France narrowly survives Schliffen but is soon hammered on by the German-Italians and starved for manpower by an overlong Western Front, which sucks in the bulk of British forces too, otherwise dispersed among many fronts. Russia staggers from the German-Austro-Turkish onslaught. Germany sees victory close in sight enough to drop unrestricted submarine warfare for good the first time neutral America makes unhappy rumors. I would bet my savings on the CPs in the scenario.