This is less a question about SQL Injection itself, and more about this particular ML based implementation.
I had to look at the code to understand better what the author tried to say with this example. To the best of my understanding, this is actually a very poor example, let's remember this is a tool supposed to execute SQLi attacks, not to just run ...
Although your whole company no longer uses a VPN; you can still use a VPN. You can provision a VPN that is only used for this scenario:
Create a VPN server (plenty out there to choose from)
Connect the destination database server to that VPN as a client
Configure each company user to that VPN as a client
Each company user connects to the VPN when they ...