Howto disable Postgres listening on TCP?
Maybe it is not the finest Solution / Answer to my question, but at least it will point anybody (facing the said challenge I had in my original question)

To disable listening on TCP/IP network I used this command line option when starting the server application:

postgres [other arguments] -c listen_addresses=''

Addition:
The remaining open udp 127.0.0.1:38860 connection is supposedly linked to the 
purpose of the the statistics collector subprocess as suggested on postgresql.org