The only way to add new fields to duplicates search result page is to add those fields as attributes to duplicates search rule (see screenshot http://prntscr.com/qzvpug).
But also we have a suggestion registered to our R&D team so to add new feature of adding custom fields to duplicates search result page and it should be implemented in one of future releases. I will also notify them about your community post so to rise the priority of the main problem. Thank you for helping us to make our application better!
