Not very likely. The kind of upheaval needed to let Hungary secede from A-H would also allow Hungary's very large minorities to secede.
Magnum's idea is probably the only chance. Let's say the Central Powers win WWI; then Germany goes ahead with its plan to overthrow King Ferdinand of Romania and the liberals, installing a conservative regime under a new German King (probably Friedrich Karl of Hesse). This is arguably necessary for the AHC since any other Romanian government will be willing - and far more able - to help the Romanians in Transylvania.
After, A-H dissolves, but the German Empire is still standing. Hungary - being large, in a geographically important position, and being one of the few semi-stable creations of the new Mitteleuropa - occupies a key position in Germany's alliance system, and German support lets it survive the next few decades with its borders unchanged. During those decades, Hungary has the opportunity to build up its military and weaken non-Hungarian separatism; either reforming to accommodate the minorities or violently suppressing and resettling them.