jmarreros

This Plugin allows to use an external image as Featured Image, this can be especially useful if you house your images in another location.
This Plugin is compatible with Nelio External Featured Image Metadata, so you can reuse your data in case you want to uninstall Nelio Plugin.

External URL Featured Image

It is what I was looking for: simplicity.

$external_image = get_post_meta( $post->ID, '_dcms_eufi_img', true );

Works well for me

Use an external url image as Featured Image for your posts, pages, and other kind of post types.

Dan Griffiths

Adds a robust third-party product system to Easy Digital Downloads. When activated, adds new fields to the Download Prices meta box allowing you to specify redirect details.
External Products is based on the extension of the same name by WebDevStudios.

Easy Digital Downloads – External Products

Was looking for exactly this: an option to add third party plugins on my own EDD shop. 

Perfect

Adds a robust third-party product system to Easy Digital Downloads

External URL Featured Image vs Easy Digital Downloads – External Products