Is there any way to write a using statement without instantiating the IDisposable immediately?

For example, if I needed to do something like:

using (MyThing thing)
{
    if (_config == null)
    {
         thing = new MyThing();
    }
    else
    {
         thing = new MyThing(_config);
    }

    // do some stuff

} // end of 'using'

Is there an accepted pattern for cases like this? Or am I back to handling the IDisposable explicitly again?