I personally prefer making them want to be at home with love, not food, as the latter can have some nasty side effects!! Do you know if he ever gets in your neighbours house? There is obviously something that makes him want to be out more, and at the moment, it could just be the weather, mine are all out a lot more at this time of year, and come winter, they are happy to be back in the house.
Thanks for that Hippy - I just thought it was the salt content that meant ham wasn't a good thing for cats.