Video tutorials not working on sub-sites?

I want to show the video tutorials on my client sites. However, it produces an error when viewing on any other site: Access Denied - Please check site registration.

Our client sites are (will be) each on their own domain.

Obviously only my main domain has been added, but I cannot find an option to add any other domains. Even if I could find the option, would it really be necessary to add every single domain? This could be easily forgotten by our employees, thus resulting in a broken video area.

Couldn't you make it so that verification is done based on the main WPMU DEV subscription or something like that?