Actually, it might be pretty easy with a post-1900 PoD. Have the CPs win WWI, then let Austria-Hungary collapse. It's conceivable that Croatia might try to break away from Hungary. You'd need people in charge of both Germany and Austria that don't really believe in continuing the Habsburg state and do believe in Austria (and Bohemia) winding up as part of the German Empire.
In that case, you might see Croatia (and by this I mean both the Hungarian and Austrian parts) walk away with Bosnia, Cattaro and a few other bits with Vienna's blessing (since it's going to remain a German client anyway). The status of Istria (and, by extension, the rest of Küstenland) is a bit questionable, as it might remain Austrian/German ... or it might wind up in Croatian hands. It might be given to the Croats in order to drive a further wedge between Croatia and Italy, forcing Croatia to turn to the only Great Power available for protection, Germany. Then again, it could be a 'breathing hole' into the Mediterranean for Germany.
Of course, this scenario would pretty much require a civil war as I somehow doubt the Hungarian nobility would let any part of what they viewed as Hungarian lands go. I suppose Croatia is a bit better off than Slovakia or Transylvania since it always had something of a unique status in the Empire and the Hungarian half of the monarchy, but I doubt they'd be allowed to leave just like that, even with the blessing of Berlin and Vienna.
All in all, it requires a lot of what-ifs to work, but it's the best I can think of right now, short of a PoD way back in the Middle Ages.