Depends on what you'll try to achieve with the application.
The console is written with GWT (for questions: see the BPMC forum). Additions could be easy, if you know GWT and if the changes are minimal.
Otoh, if you need to integrate eg. a task list in your own application, it might be a better idea to use jBPM in the embedded way (ie as a plain jar)
Thanks for your response, Joram
I'll be using a "standalone" bpm by now, so I'll check GWT.
You can always try to explain your use cases in the BPM console (BPMNC) console. If your use case is general enough, it might end up in the official release, without you having to resort to custom coding.