France occupied the Duchy of Savoy for more than 20 years during the Italian wars (1536-1559). Let's imagine the final peace with the Habsbourgs grant them the Duchy of Savoy in exchange of them agreeing not to expand in Italy (Savoy is on the other side of the Alps). Basically, an alt-treaty of Cateau-Cambresis, in which Henri II would argue his rights on the Duchy as a son of Louise of Savoy, as well as a right of occupation.
Fast forward a century later, and France starts something similar to the Reunions policy. The alt-Louis XIV establishes a Chamber in Chambery, and argues that territories formally belonging to the Duchy of Savoy should be reincorporated.:
- the city and the county of Geneva (great opportunity to fight protestantism there as well)
- the barony of Vaud
- the Bishopric of Sion and Lower Valais
This isn't the entire of Romandie, but it's a good part. It comprises the biggest cities of Romandy, Geneva and Lausanne.
Alternatively, France could keep some of the territories it got during the Revolution:
- Geneva
- the whole of Valais as the department of Simplon
- the prince bishopric of Basel, now consisting most of the French-speaking canton of Jura, and which was integrated in the Haut-Rhin department (after the annexation of the Rauracian sister-republic).
- the principalty of Neuchâtel