We'll create fresh WordPress site with Multisite Featured Image installed. You have 20 minutes to test the plugin after that site we'll be deleted.
Multisite Featured Image changes the box of the featured image for all sites. It can be used also in a single instance of WordPress and not a MU installation.
This plugin changes the box in the way that the default pop-up is replaced with the classic Media Uploader where you can choose images. Images From URL do work.
For a greater Multisite experience you can combine this plugin with the Network Shared Media plugin and have a complete Media Sharing site.
Read about it on this article.