Faking the base value

I have the following classes:

public class MyBase
{
    public virtual int DoMe()
    {
       return 10;
    }
}

public class MyDerived:MyBase
{
    public override int DoMe()
    {
       int meBased =base.DoMe(); //u need to find a way to mock this statement;
      return meBased+1;
    }
}

Given a mock instance of MyDerived, the question is how can I mock the base class of MyDerived? This is because in my derived method, I need to take the value returned from the base class and perform additional manipulation. How to mock whatever so that the following test passes:

public void DoMe100()
{
    MyDerived myDerived = Isolate.Fake.Instance<MyDerived>(Members.CallOriginal);
//mock anything to make sure the test passes here
   Assert.AreEqual(100, myDerived. DoMe()); 
}

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YAMAHA DSP-1