I was able to achive what I needed by doing the following:

1. I create the Custom Attribute SortManyColumnsAttribute

   [AttributeUsage(AttributeTargets.Class)]
   public class SortManyColumnsAttribute : Attribute
   {
   	public String sortColumn { get; private set; }
   
   	public SortManyColumnsAttribute(String sortColumns)
   	{
   		sortColumn = sortColumns;
   	}
   }

2. I added the Attribute to my table in question with the string comma separated value representing the [entity].[columnname] to sort:

[MetadataType(typeof(ScopeOfWork2WorkItemMetadata))]
[SortManyColumns("ScopeOfWork.Description, WorkItem.Description")]
public partial class ScopeOfWork2WorkItem

      3. Then modified the extender class SetInitialSortOrder as follows (forgive the programming is raw and needs to be cleaned up):

string attrs = table.Attributes.OfType<SortManyColumnsAttribute>().Select(s => s.sortColumn).FirstOrDefault();
if(!String.IsNullOrEmpty(attrs))
{
	String[] sort = attrs.Split(',').ToArray();
	OrderByExpression order = new OrderByExpression()
	{
		DataField = sort[0].Trim(),
	          Direction = SortDirection.Ascending,
	};
	for(int i = 1; i < sort.Count(); i++)
	{
	      ThenBy then = new ThenBy
		{
				DataField = sort[i].Trim(),
				Direction = SortDirection.Ascending
		};
		order.ThenByExpressions.Add(then);
	}
	queryExtender.Expressions.Add(order);
}