How can subscribers team up with trial accounts?

[Viconia Tremere]

How can can active players (accounts with subscription), team up with friends they invited with a trial accounts?
It'ld be easier and more productive when trial players can familiarise to the game while playing alongside friends with an active subscription.
If it'ld be a population issue, why not limit the toons a subscribed player can have on the trial server to 1?

well, nvm ... aparently trial players can join on the other shards too, lol