ATL / WTL / STL

class IFirstFwd : public IFirst {
public:
    HRESULT Test() {
         return IFirst_Test();
    }
 
    virtual HRESULT IFirst_Test() = 0;
};
 
class ISecondFwd : public ISecond {
public:
     HRESULT Test() {
         return ISecond_Test();
     }
  
     virtual HRESULT ISecond_Test() = 0;
};
 
class CYourComClass : public IFirstFwd, public ISecondFwd {
public:
     HRESULT IFirst_Test() {
          ...
     }

     HRESULT ISecond_Test() {
          ...
     }
};

template <typename T> 
class IFirstFwd : public IFirst {
public:    
     HRESULT Test() {
         return static_cast<T*>(this)->IFirst_Test();
     }
};
 
template <typename T> 
class ISecondFwd : public ISecond {
public:    
     HRESULT Test() {
         return static_cast<T*>(this)->ISecond_Test();
     }
};
 
class CYourComClass : public IFirstFwd<CYourComClass>, public ISecondFwd<CYourComClass> {
public:
     HRESULT IFirst_Test() {
          ...
     }

     HRESULT ISecond_Test() {
          ...
     }
};

class ISecondFake {
    // Copy the methods from ISecond and past it here
    // Prefix all mthods with ISecond_
    virtual __stdcall HRESULT ISecond_Test() = 0;
};

class CYourComClass : public IFirst, public ISecondFake {
public:
     HRESULT Test() { // IFirst version
          ...
     }

     HRESULT ISecond_Test() {
          ...
     }
};

CString strYourString = "data";
Vc6Function(strYourString);

void Vc6Function(LPCTSTR lpszString) {
   CString strLocalString = lpszString;
   ...
}