Create a new account under a fictitious name—then the user won’t know who viewed their stories. To make the account look authentic, you can set it up like a real one: add photos, post a few times, and write a profile description.
Fake accounts can be used to view stories on private profiles. Most specialized services do not have this feature — they only show stories that are open to everyone. In order to view content on a private profile, its owner must accept a subscription request from your fake account.