He needs either vast support from Austria in 1697 election (mostly cash for bribes) or wife with blood connections with Polish monarchs (that part is not easy considering the fact that Polish Vasas are gone completly, in male and female line and Sobieski is pro-French).
Austrians supported another duke in their service, Charles of Lorraine in 1669 and 1673 so it is not unthinkable.
Frederick Augustus must be neutralised somehow (dead?). Jakub Sobieski was idiot and Conti was unacceptable for Polish neighbors, Savoy could be compromise candidate in such case.
If Savoy is elected...
Effects on War of Spanish Succession and Great Northern War would be interesting.
France would do better without Savoy in Austrian service. OTOH Frederick Augustus joined GNW as Elector of Saxony, not as King of Poland, and his goal was conquest of Swedish Livonia-he wanted to give it to his son as heteditary duchy to increase his chances in future election. If there is no siege of Riga Charles XII instead of wasting time in Poland would continue camping against tsar Peter, propably leading to Russian collapse comparable to Time of Troubles.