Ellipsis "..." from outline-mode: how to react to mouse-1 events?

[David Reitter]

How would one go about creating an overlay for every "..." ellipsis  
displayed in lieu of invisible portions of text?

I'd like to get outline-minor-mode to allow me to click on the  
ellipses to show/hide the entry (the key bindings used in outline- 
minor-mode are way too awkward).
One can change the ellipsis itself:

(set-display-table-slot standard-display-table
                         'selective-display
                         (string-to-vector "more..."))

but this way one cannot add properties or overlays, since the display  
table contains character vectors.

So what would be the best method?

Thanks
- David