There isn't, unfortunately. The only workaround I was able to come up with was to iterate through the DynamicXml and store it all in a list of generic objects, then sort from there. The following example sorts training classes stored in the DataType Grid by date, then writes them out grouped by month:

@if (Model.classes.GetType() == typeof(DynamicXml) && Model.classes.Count() > 0)
{
    List<dynamic> classes = new List<dynamic>();
    
    foreach (dynamic c in Model.classes)
    {
        DateTime date = DateTime.Now;
        // If the date is blank, use today's date.
        
        try
        {
            date = Convert.ToDateTime(c.date.InnerText);
        }
        catch {}
        
        string month = date.ToString("MMMM");
        
        var training = new {
            Date = date,
            Month = month,
            Title = c.title.InnerText,
            Link = c.link.InnerText,
            Instructor = new {
                Name = c.instructor.InnerText,
                Link = c.instructorLink.InnerText
            },
            Location = c.location.InnerText
        };

        classes.Add(training);
    }

    classes.Sort((x, y) => DateTime.Compare(x.Date, y.Date));
    string currentMonth = classes.First().Month;
    
    <h4>@currentMonth</h4>
    <ul>
    @foreach (var c in classes)
    {
        if (c.Month != currentMonth)
        {
            currentMonth = c.Month;
            
            @Html.Raw("</ul>");
            <h4>@currentMonth</h4>                  
            @Html.Raw("<ul>");
        }
        
        <li>
            @c.Date.ToString("MM-dd-yyyy") | <a href="@c.Link">@c.Title</a> | @c.Location | <a href="@c.Instructor.Link">@c.Instructor.Name</a>
        </li>
    }
    </ul>
}

Hope you find this helpful!