Working with non generic parts of a generic interface

Hi consider the following code.

public interface IStuff<T>
{
    IList<T> Items { get; set; }
    IsExpanded { get; set; }
}

public interface IBar
{
    string Name { get; set; }
}

public interface IFoo : IBar, IStuff<IBar>
{
}

public class MyClass : IFoo 
{
    public Name {get;set;
    public IList<IBar> Items { get; set;}
    IsExpanded { get; set; }
}

When I use this, what I'm actually going to is is populate MyClass.Items with instances of IFoo, this is allowed as IFoo implements IBar, so all is good.

However there is a method that I'm working inside a control, which does not know and should not know about IBar. It only needs to know about IStuff<> Specifically that there is a list and a property.

When I'm working with the Items, I'm going to detect if the item implements IStuff like this.

public void ProcessItems( object item )
{
    IStuff<object> stuff = item as IStuffobject>;
    stuff.IsExpanded = true;
    foreach( var childItem in stuff.items )
    {
        ProcessItems( childItem );
    }
}

The problem here is that the cast to IStuff does not now, it returns null. What I want to do is work with the genric part of the interface only, I don't care what the T is.

The question is how do I replace

IStuff<object> stuff = item as IStuffobject>;

so that I can work with the items declared in the IStuff<> interface?