public class SqlBulkCopy 
{
    // Existing members left out
    
    public SqlBulkCopyOrderHintColumnCollection OrderHintColumns { get; }
}

// New class
public sealed class SqlBulkCopyOrderHintColumn {
    public SqlBulkCopyOrderHintColumn(string column, System.Data.SqlClient.SortOrder sortOrder);
    
    public string Column { get; set; }
    public SortOrder SortOrder { get; set; }    // throws ArgumentException on SortOrder.Unspecified
}

// New class, same shape as SqlBulkCopyColumnMappingCollection
public class SqlBulkCopyOrderHintColumnCollection : System.Collections.CollectionBase {
    public SqlBulkCopyOrderHintColumn Add(SqlBulkCopyOrderHintColumn bulkCopyOrderHintColumn);
    
    // throws ArgumentException on SortOrder.Unspecified
    public SqlBulkCopyOrderHintColumn Add(string column, SortOrder sortOrder);
    
    public void Clear();
    public bool Contains(SqlBulkCopyOrderHintColumn value);
    public void CopyTo(SqlBulkCopyOrderHintColumn[] array, int index);
    public System.Collections.IEnumerator GetEnumerator();
    public int IndexOf(SqlBulkCopyOrderHintColumn value);
    public void Insert(int index, SqlBulkCopyOrderHintColumn value);
    public void Remove(SqlBulkCopyOrderHintColumn value);
    public void RemoveAt(int index);
}

using (var sqlBulkCopy = new SqlBulkCopy(connection)) {
    // leaving out other options
    
    sqlBulkCopy.OrderHintColumns.Add("Column1", SortOrder.Descending);
    sqlBulkCopy.OrderHintColumns.Add("Column2", SortOrder.Ascending);
    sqlBulkCopy.OrderHintColumns.Add("Column3", SortOrder.Descending);
    sqlBulkCopy.DestinationTableName = "Table1";
    sqlBulkCopy.WriteToServer();
}