When you import your clients, just add a column to your spreadsheet with a date in the format of YYYY-MM-DD, using a specific date in the past.
Then choose that column as the "Effective Start Date For Content Delivery". This will start everyone as if they signed up on that date.
Make sure at least one episode is scheduled to go out on "Day 0". If there is no content available, then it won't show the access the content link.
See also: http://support.nanacast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=276
