Hi William,
You can do this by constructing a query string with all the values you want to populate and then using the inline function fn-GetQueryString.
When an incomplete form is saved, you would construct the URL to the Nintex Live form and append the values of all the fields to this string. Then inside the form, you want to set the default value of each field with the fn-GetQueryString function. It's a bit of work but certainly works. One pro tip - don't use the shortened URL feature when publishing the live form - you need the full URL.
Dan Stoll wrote about this here: http://www.sharepointpub.com/nintex-forms-reading-query-string-values/
Cheers,
Chris