I wish I had an answer for you. I would like to find out for myself as well, how it works out.
My best guess would be to be as specific in your request as possible; include in your correspondences with the Presidency that you would like the new sealing to be in the month of _____, that you need at least 10 (+/-) weeks after the sealing cancellation to book your wedding reception arrangements so all goes well, so you are hoping and praying to recieve their approval answer by _______. I'm sure it wouldn't be good to pressure them or be demanding, but politely explaining your dilemna never hurts. ..."the squeaky wheel gets the grease."
I do know it is difficult to get a cancellation, but if the reason is valid (like abuse, in my case), I think there is a better chance of approval.
Good luck, and I hope your new marriage is everything you hope for.