Install old version via TestFlight

For internal testing we want to install an old version on a device of someone who's UDID is not in the list. Via TestFlight I can add the email of this person in order for him to download the newest version (via internal testing), but I was wondering if it would be possible to enable him to download and install a specific old version?

I've seen this page: how to install previous version on TestFlight but it is rather old and the suggestions are incorrect.