Since the specialization has to agree with the base template on the return type, you can make it so by adding a “return type trait”, a struct you can specialize and draw the true return type from:
// in the normal case, just the identity
template<class T>
struct item_return{ typedef T type; };
template<class T>
typename item_return<T>::type item();
template<>
struct item_return<float>{ typedef int type; };
template<>
int item<float>();
Live example.
Note that you might want to stick to the following, so you only need to update the return-type in the item_return specialization.
template<>
item_return<float>::type foo<float>(){ ... }
// note: No `typename` needed, because `float` is not a dependent type