Image in post also used as featured image

Hello!

Is it possible to use an image added to a post with nexcellent button (so with this shortcode [singlepic id=981 w=250 float=right]) also as featured image of the same post.

Or the question could be, how can I set the featured image of a post using image saved in Nextcellent gallery?

Thanks

https://wordpress.org/plugins/nextcellent-gallery-nextgen-legacy/