struct EnumHolder : public QObject { 
    enum Enum { Value1, ... };
};

struct Foo : public QObject {
    Q_ENUMS(EnumHolder::Enum); // this should not be needed!
    Q_PROPERTY(EnumHolder::Enum property READ property WRITE setPproperty NOTIFY ...)
...
};

Item {
    Foo { property: EnumHolder.Value1 }
}