Transact SQL :: Table Lock Time Scope

I have a query which is part of bigger transaction:

;WITH CTE(
SELECT id, q,
totalQ=SUM(q) OVER (ORDER BY id ROWS UNBOUNDED PRECEDING)
FROM dbo.myTable WITH (UPDLOCK, ROWLOCK)
), CTE1 AS(
SELECT id, q_take=CASE WHEN c.Total<@qRequired THEN c.q ELSE
@qRequired-c.Total+c.q END FROM CTE
WHERE (CASE WHEN c.Total<@qRequired THEN c.q ELSE
@qRequired-c.Total+c.q END)>0
)
UPDATE t set q-=c1.q_take FROM dbo.myTable t INNER JOIN CTE1 c1 ON t.id=c1.id

Because CTE query is executed separately of update query I must put UPDLOCK hint, otherwise myTable could be changed while my query executes by some other user.(I have snapshot row committed transaction).

The problem is that my hint will hold lock on rows of myTable until the end of outer transaction(the bigger one).

But I need lock only for the time of this small query execution. What would be the best way to achieve that?