Actually that is sort of how it worked out. Played another few hours after I posted that last night. First Austria cancelled our alliance because they suddenly got the claims on Northern Italy mission. *doh* It looked kind of grim for a minute but they were involved in another war at the moment so I went into over drive to get some new allies. Fortunately Spain, Poland and a couple of breakaway French countries in the south liked me a LOT more once I wasn't allied to Austria anymore.
While my portion of Italy isn't blessed with loads of man power we are rich. I pumped everything I could into as big an army as I could get (almost equal to Austria's) and settled in to wait. If they wanted to attack I would meet them in the mountains and hope to hold them off till my Austrian hating allies could get into the war. As it would happen though that didn't come to pass....at least not yet.
After Austria got a white peace from the Ottomans they got pulled into a war with most of Europe due to some entangling alliances. I didn't get called in by anyone, probably because I had allies on both sides? Not too sure about that. With a few minutes to breathe though I noticed that what was left of Switzerland was now only allied with Tuscany. If I declared on Switzerland they could only call Tuscany in and they in turn couldn't call anyone.
Long story short by the time Austria got out of that war, somewhat battered and with depleted manpower, I had the time for two quick wars against Switzerland and Tuscany. At the end of those the two remaining provinces of Switzerland are my vassal state, I have taken Siena, Rome and Urbino from Tuscany and the later is now reduced to just their home province and two bits of Naples (Abruzzi and Bari I think.)
Then I realized it was four in the morning and went to bed. *doh*