Why does it need to be all French banks? The French government could establish a special class of bank for domestic business, that isn't subject to international pressure except pressure applied to the French government itself. They should be able to find a way that a judge in Europe, living in Europe, paying European taxes to European governments, paying rent to a European landlord, doesn't have to give a shit about what America thinks.

This is a tractable problem, except for the lack of political willpower to create a solution.