You can do it with some method-by-method boilerplate.
class A {
public:
virtual int methodA() = 0;
virtual int methodB() = 0;
virtual int methodC() = 0;
};
class B { //B implements A.A() and A.B()
public:
int methodA() { return 0; };
int methodB() { return 0; };
};
class C : public A, public B {
public:
int methodA() { return B::methodA(); }
int methodB() { return B::methodB(); }
int methodC() { return 0; }; //C implements A.C()
};
Demo: http://ideone.com/XDKDW9