I have this set up on an OpenWRT router with multiple remote endpoints used for different devices. Our phones go to a hosted Wireguard server in one city, PCs to an OpenWRT router in a different location, and IOT devices that aren’t blocked and guest devices exit access the Internet locally.

Policy Based Routing on OpenWRT makes this possible. As long as the remote server is set up to allow your WG devices to access the Internet you should be able to achieve what you want to do without further control of that server.