As you know, the French meal has been classified as an intangible world heritage by Unesco, so the problem is not to do it or in the way of doing it (sharing the dishes), but is from a point of cultural view. Restaurant staff attached to these traditions may misunderstand this.
If, moreover, they suspect that you want to save money by ordering a dish for 2 (when in their eyes you are rich Americans) imagine what will he think. That you would like to save 5 Euros with a meal that has become a World Heritage Site when you've traveled thousands of miles to get it?
They may not be too friendly with you during the meal. LOL
So, whatever the way, the important thing is to communicate and explain when ordering (with a smile), your problem to the waiter, just like you did by posting this message.
And you may have a new friend, especially if you let him know you enjoyed your meal, even a shared one.