Thanks for the feature request. We do not have the option to add custom columns right now, but what you can try and do is use either the "Notes" or the new tagging feature for grouping your partners.
To add the "Notes" column just right-click on any column's header in the workspace and select it from the list. As for the tags you can learn more about that here:
http://www.link-assistant.com/news/tags ... tware.htmlHope these features are of some help for now!
