Hello!
Sadly, there is no such option. The character transfer mechanism for New Game + was implemented for the server owner only (after requesting to start the New Game +, the owner's data is temporarily stored on the client side and after logging in on the local server the client is requesting to restore this data in the new world into the new character; the same mechanism cannot work for other players).
Unfortunately, it's not possible for us to quickly rework it to support the transfer of all the characters registered on the server—it requires a totally different mechanism...
As a workaround, the local server's owner can use cheats to add learning points and skills to any registered character on the server. Press `~` to open the console then you can use the following commands:
Set Learning Points to 10000:
/player.setLP 10000 PlayerNameHere
Set all skills to level 10:
/skills.setAll 10 PlayerNameHere
Set specific skill to level 10:
/skills.set Lumbering 20 PlayerName
(you can use autocomplete; use vertical arrows, Tab and Enter to navigate the autocomplete options)
Regards!