Hi,
I hope this can help you:
PI 7.3 – Adapter User-Defined Message Search without TREX
And the technical documentation says that it just support asynchronous messages, even in my experience i can i that i have seen working this in asynchronous messages implemented with ccBPM....
http://help.sap.com/saphelp_nwpi711/helpdata/en/48/c85598f63335bfe10000000a42189d/frameset.htm
I hope i have solved your doubt, if not i can share you more details...
Best regards,
Azael