Try this:
SELECT CUSTOMER_ID, MAX(FIRSTNAME) AS FIRSTNAME, MAX(LASTNAME) AS LASTNAME ...
FROM
(
SELECT CUSTOMER_ID,
CASE WHEN DBCOLUMNNAME='FirstName' then DATA ELSE NULL END AS FIRSTNAME,
CASE WHEN DBCOLUMNNAME='LastName' then DATA ELSE NULL END AS LASTNAME,
... and so on ...
GROUP BY CUSTOMER_ID
) TEMP
GROUP BY CUSTOMER_ID