My last post was kind of confused - must be because it was just before lunch break...
I got it to work by now, though. I used the EventManager and my existing acknowledge actions. The 'missing link' was my misunderstanding that the private EventManager.setHandlers() is not a 'simple' setter, but instead creates the runtimes from EventHandlerVO's for a given EventInstance. With it, I was able to generate a Map<Integer, List<EventHandlerRT>> that maps events to their handlers. The acknowledge actions of the EventHandlerRT's matching a given eventId are then run in the manner of the existing actions.
I do not know whether my approach is a wise one - it works atm, but untested.
Thanks for the event manager hint Matthew.
Best Regards,
Michael