Casting Smart Pointers

Hey all, Are there any well-known methods for casting between smart pointers of different types? e.g.:

class A
{
};

class B : public A
{
}

// exactly how you''d declare a smart pointer in my engine:

#define QUILL_DYNAMIC_PTR( x ) Quill::QuillPtr >

QUILL_DYNAMIC_PTR( A ) PtrToA = new A;
QUILL_DYNAMIC_PTR( B ) PtrToB = new B;

// this is impossible, due to C++ type technicalities
QUILL_DYNAMIC_PTR( A ) CastedB = PtrToB;

 

So far as I can understand, the only way to do such a thing would be to reimplement my smart pointer class to deal with such cases (at the moment my smart pointer class (QuillPtr) remains the same, whether dealing with new/delete allocated memory or COM pointers - only the RefCounter used by the QuillPtr ever needs to be reimplemented). Does anyone have any ideas? I''ll provide more source code as needed Tom