[NTG-context] how to flip even pages upside down??

Hi List, I am a new ConTeXt user coming from LaTeX background. To print duplex on my printer I need to flip even pages upside down. I looked into section 3.7 "Arranging Pages" of the latest ConTeXt manual (2010-10-26). It shows how to setup very elaborate page compositions but somehow I failed to find a solution for my little problem. Any help/advice is greatly appreciated. --Leo--