How to randomize featured image for specific post?

Hello,

I am working on a website that uses the twenty fifteen theme. I would like to make a specific post a “sticky”, but since there are no featured articles on the site it’s also automatically set as a featured article.

The problem I have now is that when you first come to the site, you see this ugly striped hole and would like to fill it with featured images in such a way, that everytime the site would load, another image would be displayed above the article.

Could maybe anyone propose how such a thing could be done? I tried searching plugins, but they only allow you to create a set featured image, or galleries out of featured images, but not a set of featured images for one post, that would randomly change as you call up the site.

Thank you all for your help!