If you contact the wonderful cast members at the Disney Floral and Gift Basket Department. They have a website at
disneyflorist.com
from which you can order a small and inexpensive gift basket that
includes personalized Mickey ears. If you don't see exactly what you're
looking for on the website, give them a call at 407-827-3505 and they
would be more than happy to create something custom for you. The florist only needs a day or so notice to create most gift baskets and personalized ears, but I would probably place my order about a week in advance.
One other note, because Disney does not assign actual rooms until
guests arrive at the building, most of the time it is impossible to
have the ears waiting for you in your room. You could arrange for two
other things to happen:
1. The cast member at the front desk could hand you the gift basket as you are checking in.
2. The hotel staff could bring the basket to your room soon after your arrival.
You can discuss with the florist which option you would prefer.
Have a great trip to Disney World!