It's only possible if you can reconcile the conflicting interests in the Balkans between Austria-Hungary and Russia. Maybe a compromise in which Serbia gets Bosnia in return for which Russia agrees to leave Serbia in the Austro-Hungarian sphere of influence.
Thing is, Serbia was never especially
in any "Russian" sphere of influence that threatened A-H. The moment it gained economic independence from Austria was when it carved the railways corridor down to Salonika in the Balkan Wars, but the Austrians had lost their overbearing power in Belgrade well before that by general apathy. In 1885, Serbia was their man; in 1903, they'd clearly lost their grop; 1908 was a bungled attempt to restore it. Russia was never really involved.
The Austrians perceived any Serbian/Slavic state in Bosnia a direct threat in and of itself - a kind of domino effect. That's why as early as 1875-6, they were asserting their right to first purchase. Given that it's impossible to pinpoint just when Serbia left the Austrian sphere, it's hard to barter this in exchange for something the Austrians objected to so stringently.
And what does Russia get from such a deal, anyway? They never really cared that much about Serbia.
Romania could then go into Austria-Hungary's sphere of influence or Russia's (could go either way)
But Austria
can't permit the permenant establishment of Russian (hence Slavic) power on the Danube. They always did much more of their communication with the wider world through the Iron Gate than Trieste, so they can't put that kind of economic blackmail-power into the hands of a Slavic state. Hungarians wouldn't stand for it.
while Bulgaria and Greece go to Russia so it can have access to the Aegean Sea. A division of spheres of influence like this one (or somewhat differently) could settle the problem.
The Russians (and indeed the Austrians) were thinking of more than physical power and influence. The Russians, indeed, failed in early attempts to build a formal sphere-of-influence in Bulgaria and thereafter largely gave up on the idea.
What lay at the root of it was the Ottoman straits. The Tsarist economy worked by exporting grain to raise the capital that would import expertise and machinery for its growing industries. The best grain-country is Ukraine and South Russia, and the industrial heartland was the Donbas in Ukraine and South Russia. When the Ottomans closed this bottleneck
very briefly for military reasons during the Italian war, the Russian economy took a visible dip. Lots of Russian diplomats at the time acknowledged that everything was about the straits: they had to be kept in Ottomans hands, because the Ottomans could be blackmailed. As far as the Ottomans were concerned Russia was a big, scary neighbour with ties to the Armenian terrorists that could invade whenever it liked, so the Russians were willing to accept Ottoman straits - never Greek or Bulgarian -
unless the Ottomans somehow gained a sponsor that would put them in a position to stick one to Russia with impunity.
That's where Germany comes in If Russia had allowed Serbia to be destroyed in 1914, it would have left Austria, Bulgaria - drifting from Russia and a growing field of German investment - and a couple of German kings between Germany and the Ottomans. Note that some Russians were willing to contemplate it in 1908, when Germany-Austria-Ottomans was just how things were already and the consequences of the Young Turk revolution weren't yet apparent.
The gauntlet was thrown not by Austria in the Balkans, but by Germany, in building the Berlin-Baghdad railway. The Austrians and Russians had gotten on perfectly well in the Balkans under German supervision for decades before 1908; and although he was acting without the full consent of Petersburg, the Russian dude in 1908 (I forget his name, began with an I?) was basically willing to let Serbia go hang.
On the other hand, a Germany that
doesn't build the railway and accepts an Ottoman Empire that says "How high?" when Russia says "Jump!" wouldn't find it too difficult to ally with Russia, circumstances favouring...
The second issue is not having Wilhelm II behave like a dick. Either change him or don't have him around to screw stuff up. You decide...
Essentially, I'm saying that this issue is the same as the first. The problem is slightly more extensive than Wilhelm II himself: an impressionable Kaiser desperate to be popular combined with chancellors engaged in a mad parliamentary balancing act to replace Bismarck's wise strategy that Germany should keep the peace by asking for nothing not by asking for
something but by asking for
everything. If Germany had played chums with Russia and built a fleet, or invested in the Ottoman Empire and not built a fleet, she'd have secured a permenant increase in her power, influence, and prestige. As it was, she did both. We know how well that worked out...
.