SSRS 2005 Return the parameters that do not return a matching record

SSRS 2005 Return the parameters that do not return a matching record

I am using SSRS 2005. I have a report that has a single parameter
"@Serial". Our support technicians enter computer serial numbers into the
parameter field and generate a report returning the matching records from
the database table. The count of serial numbers is not hard set and ranges
from 1 to 100++.
My ultimate goal is to list the serial numbers that do not return a
matching record.
In SSRS I have tried using the =JOIN(Parameters!Serial.Value,",") to list
all of the parameter values (serial numbers) into a text field. This works
fine to list ALL of the parameters passed but I do not know the correct
expression to convert the list so it only contains only the un-matched
serial numbers.
It was suggested that I use a Left Join in the SQL query, however, I don't
know how to get the parameters entered by the technician into a temp table
in SQL so that I can Join the two tables.
Any help on either method is appreciated, and alternatives to these two
methods are welcome.