You can direct your SOA or IDOC to the PI system instead of the target system. The fact that you are using a PI system does not make a difference on how you actually replicate the data. The PI system is just "another" system that you can talk with. In fact, it is more convenient to send IDOC's to PI since the PI system "understands" ECC naturally.
In any case, you should start a new thread given this one is 2-year old. You should also refer to this thread in your new thread.