We had this done for our family (5 adults, 4 children) when we were staying at the GF. I called the concierge desk, gave them my credit card #, the hat sizes, and the names for each.
It took us awhile to check in (room wasn't ready even after 4pm), but when we finally got there, yes, the mouse ears were waiting on the coffee table.
It can be done...call the hotel and ask!