Override them like Michael Suggests above and to prevent folks from using the overridden (sp?) methods, mark them as obsolete:
[Obsolete("These are not supported in this class.", true)]
public override void dontcallmeanymore()
{
}
If the second parm is set to true, a compiler error will be generated if anyone tries to call that method and the string in the first parm is the message. If parm2 is false only a compiler warning will be generated.