Can I Set A Variable Equal To A Case Statment?

I have a case statement I need to refer to several times in my select statement and it's quite long. I would like to just refer to if by name. I tried to create a variable for the Case statement (see below) but I get an error that says, "
Sub query returned more than 1 value. This is not permitted when the sub query follows =, !=, <, <= , >, >= or when the sub query is used as an expression."

USE GP05
GO

DECLARE @EmpID nvarchar (6)

SET @EmpID = (SELECT CASE WHEN NOT(dbo.BE010130.EMPID_I IS NULL) THEN dbo.BE010130.EMPID_I
WHEN dbo.BE010130.EMPID_I IS NULL AND NOT(dbo.UPR00500.EMPLOYID IS NULL) AND dbo.UPR00600.EMPLOYID IS NULL THEN dbo.UPR00500.EMPLOYID
WHEN dbo.BE010130.EMPID_I IS NULL AND dbo.UPR00500.EMPLOYID IS NULL AND NOT(dbo.UPR00600.EMPLOYID IS NULL) THEN dbo.UPR00600.EMPLOYID
WHEN dbo.BE010130.EMPID_I IS NULL AND NOT(dbo.UPR00500.EMPLOYID IS NULL) AND NOT(dbo.UPR00600.EMPLOYID IS NULL) THEN dbo.UPR00500.EMPLOYID
END FROM dbo.BE010130 FULL OUTER JOIN dbo.UPR00500 ON dbo.BE010130.EMPID_I = dbo.UPR00500.EMPLOYID AND dbo.BE010130.BENEFIT = dbo.UPR00500.DEDUCTON
FULL OUTER JOIN dbo.UPR00600 ON dbo.BE010130.BENEFIT = dbo.UPR00600.BENEFIT AND dbo.BE010130.EMPID_I = dbo.UPR00600.EMPLOYID)

SELECT @EmpID

I can get around this by simply retyping the case statement when I refer to it in the where clause, but I would prefer not to do this. Can someone point a newbie in the right direction? I have 5 case statements in this query and it starts to look pretty ugly when you have to retype them multiple times.

Thanks!