Synchronize users in a multisite network

I found the Synchronize users plugin, but what I want is that when a new user in my multisite network registers on a subsite, he also is added as a member with subscriber level on the main site.

That way clients can also login via the main site (login widget), or can have access to main site content via their own site login.

Is this possible and how?

Thanks in advance and have a nice evening!!