After Alexander of Battenberg lost the throne of Bulgaria in 1886, Austrian Archduke John Salvator was apparently one of the leading canditates for the throne. Now as Bulgaria was in the Russian sphere of influence in the Balkans as deliniated by the Congress of Berlin, this created friction with Austria, and hence Russia worked to prevent John Salvator from getting the throne. Therefore, Ferdinand ended up getting the throne.
Now, would it be possible for Salvator to gain the throne of Bulgaria? The most likely situation I see would be Austria being more forceful and confrontantional in their diplomatic policy in the Balkans, so the government forcefully promotes Salvator for the throne. Perhaps a touch of handwavium to get Salvator chosen, but then we probably see an Austro-Russian War over the incident. Germany's stance would certainly be very important, and although I think they would support Austria, there are certainly many approaches Germany can take.
Thoughts?