possible to add columns to capi:multi-column-list-panel?

Is it possible to change the number of columns displayed in a multi- 
column-list-panel? I can't find any way to change the column  
specification once the panel has been instantiated.

If this isn't possible, could one swap an existing panel in an  
interface for a new one ? I've tried declaring an accessor for the  
panel pane and setf'ing like this:

(define-interface solution-list-interface ()
   ()
   (:panes
    (solution-list-pane multi-column-list-panel
                        :accessor solution-list-pane))
   (:documentation
    "A widget displaying solution data in multi-column-list-panel."))

(setf (solution-list-pane interface)
   (make-instance 'multi-column-list-panel
     :columns '((:title "#"
                                    :width (character 2))
                                   (:title "Word"
                                    :width (character 15))
                                   (:title "Gloss"
                                    :width (character 15))
                                   (:title "POS"
                                    :width (character 15)))
                        :visible-min-height :text-height))

But it seems like it doesn't affect the panel.

Any suggestions?

Kind regards

André