How to tell JPA to queue threads?

Hello guys!

We get a ORA-00054 from Oracle when we stress our application.
The exception looks like:
java.sql.SQLException: ORA-00054: resource busy and acquire with NOWAIT specified

The code that cause this is this JPA-code:

MyObject myObject =(MyObject)em.find(MyObject.class, id);
em.lock(myObject, LockModeType.WRITE);

What we want is that when several threads access this code they should wait in a nice line until they can set there own lock.
Now it looks like that next thread accessing this code it just get a exception back from oracle.

If I'm not wrong the JPA-code above do some SQL like:
select * from myobject where id = x for update nowait

We of course would like it to do something like:
select * from myobject where id = x for update wait

But how do we send the "wait"-param?

Right now I can not give information of what version of JPA we use. I just know that we use EJB 3.0 with JBoss 5.

Bets regrads
Fredrik