OOP: How to dynamically extend functions in superclass

I have a base class B and 2 derived classes D1, D2.

class B {
    int commonFunc();
    virtual int specifyFunc();
}
class D1 : public B {
    int specifyFunc();
}
class D2 : public B {
    int specifyFunc();
}

Now I meet a requirement that i need to extend my base class function "commonFunc()". Since i don't want to modify existing code in base class, i derived another class like:

class B {
    virtual int commonFunc();    // Change to virtual
    virtual int specifyFunc();
}
class B2 : public B {
    int commonFunc();    // A new commonFunc() to meet new requirement
}

However, D1 and D2 cannot use the new commonFunc() in B2 except I modify the inheritance hierarchy.

Here is a possible solution i figured out

class B {
    virtual int commonFunc();
    virtual int specifyFunc();
}
class D1 : public B {
    int specifyFunc();
}
class D2 : public B {
    int specifyFunc();
}
class NewD1 : public D1 {
    int commonFunc();   // Overrided commonFunc() in base class
}
class NewD2 : public D2 { 
    int commonFunc();   // Overrided commonFunc() in base class
}

Since the commonFunc() in NewD1 and NewD2 are exactly the same, this solution involves a poor code-copy

I am looking for any design pattern or solution which can dynamically extend base class without much modification to existing class.