SSRS 2008 dynamic Parameters

I am creating a report with several parameters for users to insert data into a table.  
What I would like the report to do is when the user selects 'New Service' the textboxs and data fields would be blank.  If the user selects a service they already create to update fields (inserting a new row into the table and recorddeleting the old row.)

I have created the SP for the textboxs and date fields:

IF @ClientLabId <> 'New%' BEGIN
SELECT 
 cc.Date_Service_Referral, cc.Ordering_Provider, cc.Provider_Specialty, cc.Provider_Contact, cc.Desc_of_Order,
 cc.First_Scheduled_Date_Service, cc.Attendance_Confirmed, cc.Date_Record_New_Service_Receieved,
 cc.Date_Record_Ordering_Provider_Confirmed, cc.Date_Record_PCP_Confirmed	
FROM CCMT_Service_Referral_Tracking cc
WHERE cc.Client_Service_Id = @ClientLabId 
AND cc.RecordDeleted = 'N'
END
IF @ClientLabId = 'New%' BEGIN
SELECT 
 NULL AS Date_Service_Referral, NULL AS Ordering_Provider, NULL AS Provider_Specialty, NULL AS Provider_Contact, 
 NULL AS Desc_of_Order, NULL AS First_Scheduled_Date_Service, NULL AS Attendance_Confirmed, NULL AS Date_Record_New_Service_Receieved,
 NULL AS Date_Record_Ordering_Provider_Confirmed, NULL AS Date_Record_PCP_Confirmed	
END

Select allOpen in new window

Setting the output of the query to the default values of the SSRS seems to lock the parameters and using it as the available values creates a Dropdown the will not allow the user to enter data.  Is there a way to code this so it will populate the parameters or leave them null depending on the user third choice?