1. Declare the dependency using @EJB at the class level (most EJB 3 references should cover this).
2. Use XML DD (web.xml) to declare the dependency (WebLogic 10 references should cover this).
3. Use global JNDI names (WebLogic 10 references should cover this).
Why are you using look-ups in this case in the first place?
Independent Consultant — Author, EJB 3 in Action — Expert Group Member, Java EE 6 and EJB 3.1