Sawfish popup menu key binding?

Is it possible to customize the key binding in the popup menus?

I've written this function which I'm using to popup a menu of window
names of certain types:

(defun popup-menu-of (pred)
  "make popup windows of a certain type"
  (popup-menu 
   (mapcar #'(lambda (w) 
               (list (window-name w) 
                     (lambda () 
                       (uniconify-window w)
                       (x-raise-window w)
                       (set-input-focus w))))
           (filter pred (managed-windows)))))

I can then use the arrow keys to select the entry I want.

But I would like to use C-n and C-p rather than the arrow keys. How
can I bind different keys to the popup-menu?

Thanks!
Best regards
//Petter

-- 
Sawfish ML