Easy: At the Congress of Vienna, some people advocated the idea that for historical reqasons, the Electorate of Brunswick-Lunenburg should become the Kingdom of Saxony, while the ruler of Meißen-based Saxony would as loser of the Napoleonic wars be forced to revert to the title of Duke of Meißen or Duke of Thuringia.
Let this happen.
More serious: You would probably need a Stuart-Wettin connection closer to Charles II. than the Stuart-Guelph(Hanover) one. Note that this will abort the conversion of the Saxon ruler to catholicism and their personal union with Poland, thereby significantly changing the Great Northern War, the War of Polish Succesion and other conflicts of the 18th century. Much less important *Hanover will probably not acquire Bremen-Verden from Sweden, but i can't say who might.