You can implement interface methods using the following C# syntax:

public class Foo : IList
{
    public int IList.Add(object value)
    {
        // your IList Add impl
    }
}

Doing so is called implementing the interface explicitly and by doing this, the methods will be available only on the interface.

This means that in order to call Add(object) on class Foo, you'd first need to cast it to an IList.

HTH...