Hi,
the discussion is quite old and I don't know if the problem is solved but I run into the same one.
Although there are plenty of blogs about it it took me some time to get it running.
A very good guidleine is availlable here in point 3 - Parameterized Mappings:
After finishing all the mentioned settings in MM. OM and Integration process within ESR there was still the question where to assign the name of the RFC communication channel to the parameter of the transformation step in BPM.
Answer is:
After definition and assignment of a parameter of type adapter in Repository to the integration process an empty parameter is added to the integration process in Directory. There the value of the RFC channel have to be assigned.
/Michael