Aque se te parace??

gistfile1.txt

public class ScenarioBindingConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, string language)
        {
            Scenario s = value as Scenario;
            return (MainPage.Current.Scenarios.IndexOf(s) + 1) + ") " + s.Title;
        }

        public object ConvertBack(object value, Type targetType, object parameter, string language)
        {
            return true;
        }
    }