I studied this subject for almost a day and then, bang, it hit me. I knew how to do this 2 years ago. Tried it again and found the solution. It is described here: http://livedocs.adobe.com/en_US/Photoshop/10.0/help.html?content=WSfd1234e1c4b69f30ea53e41001031ab64-77e3.html. Now I just hope I remember this earlier next time 😉