How do you call a C# function with overloaded return arguments from MATLAB?

Suppose I have the following code in C#:

public class MyClass
{
    public void MyFunction(out string str)
    {
        str = "Hello";
    }

      public void MyFunction(out int a)
      {
          a = 5;
      }
  }

Suppose I then want to call this function from MATLAB:

>>NET.addAssembly('MyCSharpDll.dll');
>>obj = myNamespace.MyClass();
>>number = MyFunction(obj);

The last call is ambiguous. I get this C# situation in an API from a third party. How can I tell matlab to call MyFunction with the return type I want?