I like your idea of pumping before the ceremony because I personally would feel a little uncomfortable nursing during the wedding ceremony itself... though I'll freely nurse just about anywhere if I don't have a bottle handy and the kid is hungry. Fresh pumped milk keeps for 8 hrs at room temp so you don't need to worry about refrigerating it if it's just for the ceremony.
For the reception, I wouldn't bother with pumped milk (once the bottle you pumped for the ceremony is gone). There has GOT to be a place to nurse somewhere... depending on your comfort level, you could nurse discretely right in the middle of the reception (that's what I would do), or if not that, there is probably a small room you could duck into somewhere (kitchen, library, lounge, etc), a bench in the hall, a closet, a phone booth, or if all else fails, there's always the bathroom... not pretty but it gets the job done (though I will warn you that I have had both of my kids de-latch and scream when a toilet flushes LOL). Many nicer hotels have chairs in the ladies room or even a lounge/powder your nose area that is perfect for nursing.
Good luck!
Where did you find your dress?
My sweet boy 8/06
My beautiful girl 10/09