Based on the definition of a hometown:
An individual’s place of birth, childhood home, or place of main residence
...there will only be one place to name.
It is unfortunate, I'm a military brat myself so I never lived in in any location for more than 4 years, with an average of 3 years per place. Instead of having multiple hometowns (which I doubt Facebook would change), may I suggest you join the "networks" for the places you have lived?