class NVBase
{
protected:

    virtual void virtualAction (void * ...) = 0;
};

template <typename RetType, typename ... ArgTypes>
struct VBase : private NVBase
{
    RetType makeBorsch (ArgTypes ... args)
    {
        RetType output;
        virtualAction (&output, args ...);
        return output;
    }
};

template <typename T, typename P>
class YourMomma : public VBase <T, P>
{
    void virtualAction (void * out_ptr ...) override
    {
        auto typed_out = static_cast <T *> (out_ptr);

        va_list data;
        va_start (data, out_ptr);

        auto arg1 = va_arg (data, P);

        //борщ среднестатистичекой мамки
    }

    //...

public:

    //...
};

class WhoreSister : public YourMomma <int, double>
{
    void virtualAction (void * out_ptr ...) override
    {
        auto typed_out = static_cast <int *> (out_ptr);

        va_list data;
        va_start (data, out_ptr);

        auto arg1 = va_arg (data, double);

        //борщ твоей сестры-шлюхи
    }

    //...

public:

    //...
};

//...

WhoreSister anya {};
YourMomma <int, double> nadezhda_srakovna {};
YourMomma <int, double> & anya_ref = anya;
YourMomma <int, double> & mamka_ref = nadezhda_srakovna;

anya_ref.makeBorsch (1.0); //борщ сестры
mamka_ref.makeBorsch (1.0); //борщ мамки