IOTL, the disastrous Italian management of the Third War of Independence is due even to the fact that Austria was willing to negotiate and cede Venetia through negotiations (France was trying to be the "dealer", which explains why in the post-war negotiations Veneto was ceded to France in the first place and then by France to Italy). From what I know, it was a war where neither of the sides were really willing to go to battle. If you take the Italian indecisiveness due to the possibility to get what they wanted without a fight, chances are the Italians fight better (not wasting the numerical advantage they had by splitting their Army in tow would have helped). So you need Austria to decisively win the two-front war against Prussia and Italy, push deep into Lombardy, but then... The population will never accept to get back under Austrian control. Central Italy will stay loyal to the Kingdom, so will the Northwest. I do not know wether the Austrians could try and send Francis II back to Naples (he was in Vienna IIRC) to incite a pro-Borbonic revolt, but given Francis' personality, I do not see this being a success.