You cannot! If a class inherit from a base class and override some methods of the base class, it's assumed that the new class extends the base class: the base class method knows how to deal with the base class, but that could not be a valid operation to be done on the inherited class!
What you can do is this:
class Base
{
public virtual void Method()
{
...
}
}
class Derived : Base
{
public override void Method()
{
base.Method();
...
}
}