I konow it's history question now. But for other googlers: you could write something like this. But this requires change in base class what makes it useless with external libraries.
class A
{
void protoX() { Console.WriteLine("x"); }
virtual void X() { protoX(); }
}
class B : A
{
override void X() { Console.WriteLine("y"); }
}
class Program
{
static void Main()
{
A b = new B();
// Call A.X somehow, not B.X...
b.protoX();
}