Unfortunately it is impossible (((


namespace ConsoleApplication1
{

public class BaseClass
{
public string Prop1 { get; set; }
}

public class DerivedClass : BaseClass
{
public string GetProp1()
{
return Prop1;
}
}

public class Program
{

private static void Main(string[] args)
{
BaseClass objBase = new BaseClass();

objBase.Prop1 = "Helllo";

DerivedClass objDer = objBase as DerivedClass;

Console.WriteLine(objDer.GetProp1());
}
}
}