I've decided to "reclaim" this day as my own and enjoy an expensive dinner.
I think this is a great place to start, and go from there. Kind of takes the pressure off of "celebrating". Take it for what it is... a very nice meal, and maybe you two can catch up and talk. I think reclaiming the day as your own is a wonderful approach.
On the side note: I'm glad he agreed to take the poly. I'll keep my fingers crossed for you that all goes well.