WebObjects/EOF/Using EOF/Custom Qualifiers
Pierre Bernard has some very cool qualifier extensions on his site: http://web.archive.org/20050215013412/homepage.mac.com/i_love_my/code.html
You might find what you need there or at least a good starting point.
The qualifiers referenced by Chuck have been folded into the Houdah WebObjects Frameworks project. More information can be found in the Wiki: