I don't think you need to alter any ORM method. I would go by doing this:

• Set Odoo to debug mode in the client. 
• Open the "search more" screen you want to alter
• Using the debug-mode find the view that has been opened
• Inherit that (xml-)view in your own module and add the column

This should give you the new view using the extra column.

Thanks for the response.

When opening the search more screen, I can't access the debug list which is in back, the window is open as modal (same behavior than creating a new civility in the client screen)