1) How much time is your method going to be executed?
2) Do you need this object to be accessible from another ejbs?
3) Are you going to use this object as a status of your method execution?
P.S. EJB is designed to be thread safe and easy for clustering. I think that your solution is going to break these things. And even if you will find a workaround I guess that it can cost you a lot of time in the future.