The use of DynamicQuery parenthesis is available as of the ES 2008.1.0623.0 release. Here are a couple of examples from our NUnit tests. Notice where the default conjunction changes come in relation to the opening/closing paren. You should be able to conditionally loop or nest things, provided you make sure you have matching opening and closing parens.

AND with an OR Loop:

EmployeeCollection collection = new EmployeeCollection();

collection.Query.Select(
    collection.Query.EmployeeID,
    collection.Query.Supervisor,
    collection.Query.Age);

collection.Query.Where(collection.Query.Age == 20);

collection.Query.Where(new esWhereItem(esParenthesis.Open));

collection.Query.es.DefaultConjunction = esConjunction.Or;

for (int i = 0; i < 4; i++)
{
    collection.Query.Where(
        collection.Query.Supervisor == i &
        collection.Query.EmployeeID == i + 1);
}

collection.Query.Where(new esWhereItem(esParenthesis.Close));

collection.Query.Load();

collection.Query.es.LastQuery:

SELECT [EmployeeID] AS 'EmployeeID',
    [Supervisor] AS 'Supervisor',[Age] AS 'Age'  
FROM [ForeignKeyTest].[dbo].[Employee] 
WHERE [Age] = @Age1 AND 
(
    ([Supervisor] = @Supervisor2 AND [EmployeeID] = @EmployeeID3)  
    OR ([Supervisor] = @Supervisor4 AND [EmployeeID] = @EmployeeID5) 
    OR ([Supervisor] = @Supervisor6 AND [EmployeeID] = @EmployeeID7) 
    OR ([Supervisor] = @Supervisor8 AND [EmployeeID] = @EmployeeID9)
)

Multiple Nesting of AND and OR:

EmployeeCollection collection = new EmployeeCollection();

collection.Query.Select(
    collection.Query.EmployeeID,
    collection.Query.Supervisor,
    collection.Query.Age);

collection.Query.Where(collection.Query.Age == 30);

collection.Query.Where(new esWhereItem(esParenthesis.Open));
collection.Query.Where(new esWhereItem(esParenthesis.Open));

collection.Query.es.DefaultConjunction = esConjunction.Or;

collection.Query.Where(
    collection.Query.EmployeeID == 1 &
    collection.Query.Supervisor.IsNull());
collection.Query.Where(
    collection.Query.EmployeeID == 2 &
    collection.Query.Supervisor == 1);

collection.Query.Where(new esWhereItem(esParenthesis.Close));
collection.Query.es.DefaultConjunction = esConjunction.And;
collection.Query.Where(new esWhereItem(esParenthesis.Open));

collection.Query.es.DefaultConjunction = esConjunction.Or;

collection.Query.Where(
    collection.Query.LastName == "Smith" &
    collection.Query.Supervisor.IsNull());
collection.Query.Where(
    collection.Query.LastName == "Jones" &
    collection.Query.Supervisor == 1);

collection.Query.Where(new esWhereItem(esParenthesis.Close));
collection.Query.Where(new esWhereItem(esParenthesis.Close));

collection.Query.Load();

collection.Query.es.LastQuery:

SELECT [EmployeeID] AS 'EmployeeID',
    [Supervisor] AS 'Supervisor',[Age] AS 'Age'  
FROM [ForeignKeyTest].[dbo].[Employee] 
WHERE [Age] = @Age1 AND 
(
    (
        ([EmployeeID] = @EmployeeID2 AND [Supervisor] IS NULL) 
        OR ([EmployeeID] = @EmployeeID4 AND [Supervisor] = @Supervisor5)
    ) 
    AND 
    (
        ([LastName] = @LastName6 AND [Supervisor] IS NULL) 
        OR ([LastName] = @LastName8 AND [Supervisor] = @Supervisor9)
    )
)