I will normally celebrate Valentines Day the day/weekend before, because I hate the fixed menus, extra cost, large crowds and long waits. We will go wherever we want, and then either have leftovers on Valentines Day, or I will cook a good meal for us.
If this isn't an option for you, then I would just order the 5 course feast, eat bites of each course, and then bag up the rest for home. Honestly, everybody is so into doing their own thing, that nobody will notice. Even if they do, who cares? Do your thing.