You can include a call-to-action in your scheduled post through Social Slingshot just like you can when posting directly on Facebook!
Adding a call-to-action button to your posts encourages the end user to click on your post and directs them to your landing page (here is more detailed into on call-to-action buttons). Here's an example:
Simply click on Advanced Options when scheduling a post and scroll down to the Action you want people to take when they see your post section: