When someone is a postdoctoral researcher, is the person directly "above" him in the hierarchy called his supervisor, or his scientific coordinator?
I have seen the term "Line Manager" used in the context of post-doctoral researchers here in the UK.
I have also seen reference made in CVs to the principal investigator for the research project to which the author contributed, e.g. "I worked with Prof. X, Principal Investigator for Project Y". The term "Scientific Co-ordinator" seems to be most closely related to this. Perhaps, therefore, the term "scientific co-ordinator" suits your purposes best.