How do I add "Flexi-task respondent" as an item property in a SharePoint library?

I have a Flexi-task, set up as "First response applies", in a Nintex workflow.  The group for whom I have built this workflow wants to see the name of the person who responded as an item property in a SharePoint library.  What action do I use, or how do I otherwise capture this information and add it as a column in a SharePoint library? Any suggestions or information would be most appreciated 

Thanks!

Stephen Billias
Communications Project Coordinator
Health New England
One Monarch Place, 15th Floor
Springfield, MA 01144-1500
413 233-3429
sbillias@hne.com