Private tweet to non-following users


I’m developing an iPhone/Android app. When a user signs in with email or Facebook we email them a welcome guide. Because the Twitter api won’t give me the user’s email, I only have the user’s handle when they sign in with Twitter. How do I send them a link to the welcome guide without effectively publicizing a list of twitter-registered users on my twitter feed? Sending @mentions from a private account won’t work because they just won’t see it.