I think the golden ticket is already set up - the solution to the cloaking technology. However, with several episodes in the mirror universe still to go, Starfleet can't use it yet. Once they return, I imagine that will be used to negotiate a ceasefire.To be brutally honest, I don't see how the Klingon War can be wrapped up so fast.
Unless it's 1) a ceasefire, or 2) Mirror Discovery unintentionally does all the dirty work for Starfleet, bringing the Empire to its knees, and the Federation takes advantage of it.
Or 3) the war is won off-screen, conventionally. A story possibility I like the least.