Databinding two way

Hey I have created a microsoft Ribbon Window in Visual studio 2010 wich works great with databinding in a one way manner.

So if I push a button a method get's triggered and the code inside get's executed, it even works with passing a parameter, now my question is how I should return a value of a method to a textbox,treeview or other control on the RibbonWindow?

I'm using this relay command class:

 public class RelayCommand: ICommand
    {
        #region Fields

        readonly Action<object> _execute;
        readonly Predicate<object> _canExecute;

        #endregion // Fields

        #region Constructors

        /// <summary>
        /// Creates a new command that can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        public RelayCommand(Action<object> execute)
            : this(execute, null)
        {
        }

        /// <summary>
        /// Creates a new command.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("execute");

            _execute = execute;
            _canExecute = canExecute;
        }

        #endregion // Constructors

        #region ICommand Members

        public bool CanExecute(object parameters)
        {
            return _canExecute == null ? true : _canExecute(parameters);
        }

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public void Execute(object parameters)
        {
            _execute(parameters);
        }

        #endregion // ICommand Members
    }
}

And than I have an other class with ICommands and methods.

like this: How can I return the param value from method ConnectionStartUp to a textbox control for example?

public class MyInputCommands
    {
        private ICommand _connectionStartUpCommand;

        private Connection connectie;

        public ICommand ConnectionStartUpCommand
        {
            get
            {
                if (_connectionStartUpCommand == null)
                {
                    _connectionStartUpCommand = new RelayCommand(
                        param => this.ConnectionStartUp(param),
                        param => this.CanDoIt()
                        );
                }
                return _connectionStartUpCommand;
            }
        }

        public string ConnectionStartUp(Object param)
        {
            MessageBox.Show("De status van deze Checkbox is: hello world" + param);
           return param

        }

        private bool CanDoIt()
        {
            //Nagaan of het command kan worden uitgevoerd.
            return true;
        }

    }