If they had to make an exception for you, they would have to for everyone...and then if it's 2 months, then why not 3 months before age 3? And then where do you cut it off? They do have the cutoff age for a reason, as someone else already mentioned, the makeup is for age 3+. Honestly if the BBB experience is going to make or break your entire trip, the best thing you could do is push your vacation dates back by two months and wait until she has turned 3 so that you will be able to have that experience with her.
If you decide to go ahead with the vacation as is, then get her a princess dress, shoes, tiara, etc and set it up at night after she's in bed, so it's waiting for her when she wakes up. Leave a special note "from Cinderella" or her favorite princess. Get her all dolled up and make a big deal about the fact that Cinderella left her this beautiful outfit. Get pixie dusted at Castle Couture in MK, ride the carousel and dine at CRT. You will have a magical day.