Multiserver setup with mysql-only server

[Croydon]

I just tried out a multiserver setup where the main host serves all the available things and a second host that is client database-only.
With this setup I recognized a problem.

If you set up a database on a database-only server you always have to enable remote access for the database as you would not be able to use it otherwise.
And as the database is not linked to a website (like it was in ispc2) you cannot automatically determine the "local" ip that is probably used to access the database.

Do you see any possibility to automatically allow access of needed ips to the database without having the client to enable remot access?

The only solution I see is to get all the ip addresses of all website-servers the client has in use and to grant access to those ips even on disabled remote access.