How to auto close popup window of UWL?

Hi everyone! I have developed a web dynpro abap application that is being launched by the UWL in a new window. How do I close the window after the web dynpro application is done processing? I cannot use exit-plugs as these don't work in the portal. If I use the portal navigation classes(absolute and relative) these ask for a target address but what I want is to close the window. Has anyone done this before? Thanks! Generous points will be awarded!