How to set role using OpenJPA

I have weblogic system libraries having javax.persistence_1.0.0.0_1-0.jar and org.apache.openjpa_2.2.0.0_1-1-0.jar.

EntityManager em = eClepRoleFactory.createEntityManager();

1. Connection c = (Connection)OpenJPAPersistence.cast(em).getConnection();
String s = "SET ROLE "role" IDENTIFIED BY "+pass;
Statement stmt = c.createStatement();
stmt.execute(s);
stmt.close();

2. em.getTransaction().begin();
Query q = em.createNativeQuery("SET ROLE eclep_hpn_role IDENTIFIED BY role55");
em.getTransaction().commit();

Note: I am able to set the role using the steps in 1, but not with the steps in 2.
Question: What is missing in steps 2, because of which I am not able to set the role. Doesn't createNatvieQuery support this feature. Please help me urgently.