From within Nestio there is no ability to feature listings on StreetEasy. See below for information from StreetEasy regarding how this can be done from directly within your StreetEasy account:
Login to your account and click the "Agent Tools" in the menu bar at the top of the page. About a third of the way down on this page you'll see the subtitle "Featured Listings." There should be an orange button that says "Learn More and get started here" just below it - click on that.
This leads you to a page that explains what featured listings do. At the bottom of the explanation is the sentence "Get started now, select your listings to promote." Click on those words.
From here you can see a list of your rentals and sales, and just to the right of each listing you'll see a white box with payment options depending on how long you want to feature for.
Make your selections, then fill in your credit card information, checkout, and you're all set!
For any additional questions about StreetEasy, contact their team directly at firstname.lastname@example.org