In SSRS, there is a limitation that you cannot pass a multivalue parameter to a stored procedure. I read a couple of ways to get around that, the best being this one from Mark Vaillancourt. The ‘Scooby Do’ references are pretty funny. Ruh roh.
In the spirit of laziness, I wanted a slightly simpler answer. I prompt the use to enter a comma separated list of customers, and parse them into a table in SQL. Then, I join that table to the customer master table in my application. Or you could do a ‘WHERE CUSTNMBR IN (SELECT CUSTNMBR FROM @MYTABLE)’