My wife often walks with a cane and sometimes has trouble walking distances. How can we arrange for one of the carts to take us from security to the gate (or lounge), etc.? Is it possible to just flag down a cart or does it have to be arranged in advance?

EDIT: We usually fly out of JFK. Typical destinations would be in Europe, such as LHR, FCO, CDG. Next trip is to MXP.