Bulk user creation

Hey, I’m in a situation where I have to create a lot of users with the Admin Rest API, create each of them with an API could make a network load.
I’m searching for a way to bulk add the users (and maybe also groups), I know I can use the export and import of a realm but that means I have to restart the service, and that’s something I can’t afford on my production environment.
Any help is appreciated.