Unlikely you will ever get this app available on a rented box. Some of the broadcasters that have agreements with Virgin would probably object, plus the box would have to have compatibility with a load of other third party kit.
VIP pack with VIVID 350. Freeview/Freesat HD, Virgin Mobile, Tesco Mobile. Cable customer since 1993
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.
I happen to think that Plex is an inferior product for media streaming but if you insist you can get an Amazon Fire TV stick for under £40 and download and install the Plex client, and some people just use their Xbox One or PS4 devices.