simple question

Hi,

I have a question regarding derived class, let' say I have a base class
class PimItem

// A MS COM interface : for people who don't know com it's an interface
struct IDispatch
{
   ...
};

// Smart COM pointers(interface)
// IContact derives from IDispatch
typedef CComQIPtr<IDispatch> IDispatchPtr;
typedef CComQIPtr<IContact,&__uuidof(IContact)> IContactPtr;

class PimItem
{
public:

PimItem(CComQIPtr<IDispatch> pIItem) {m_pIItem = pIItem};
virtual ~PimItem();

protected:

CComQIPtr<IDispatch> m_pIItem; // Smart pointer pointing to a COM interface
}

class Contact : public PimItem
{
public:

    void set_Foo(...) { static_cast<IContactPtr> (m_pIItem)->set_Foo() }
    void set_Fire(...) {static_cast<IContactPtr> (m_pIItem)->set_Fire() }

protected:

};

As you can see in the contact class ,everytime I want to access a
function I need to cast my base pointer to my derived base.
In this case wouln'd be easier to remove m_pIItem inside base class and
directly store the right pointer type inside my derived one ?