I am assuming that your breakfast is before the MK opens. WDW has breakfast buses for the numerous breakfasts throughout the World. The MK buses start around 6:30am and around 7:00am for the rest of WDW.
The driver might be able to let you off at the Poly if you let him/her know you are going there. If you must get off at the MK just take the monorail over.
Allow about 45 minutes in case you just miss a bus.