We don’t have the right bits to route traffic to IP blocks through a wireguard peer.
The best way to do this is to run something like Tailscale in all your Fly VMs. Tailscale does all the routing you’d need to make it work.
If you’re feeling bold, you can experiment with making this work on Fly, but you can’t do it with our built in Wireguard peers. You’d need to run your own Wireguard instance on Fly, figure out how to set the Fly vm that’s running it to work as a router, and then install routes through it on your other VMs.
I really want this to work some day, for what it’s worth. 