Thanks again.
I chose the way with signal events instead of timers. If I need a timer I just create an event "timerEvent_1000" where 1000 is the interval of the timer. In ProcessEventListener I catch all these event difinitions and create EJB timers. When an EJB timer is triggered I send "timerEvent_1000" to my process. So I got what I need. One thread for one call to jBPM and unlimited container managed threads.
Also I could successfully run jBPM 5 with GlassFish 3 and EclipseLink. If anyone is intrested in that I can write down the details.