I'm not sure how that works from the editor, it looks like there is some form of remote debugging (because it's needed to debug from a mobile device, however that case is particular), but I don't see where it could specify an arbitrary IP. That said, it would also require machine A to be configured so that it even accepts this connection, imagine how unsafe that would be if you could do that with any Godot-made game...
Alternatively, maybe you could use use
ssh or some other remote command line protocol to use Godot's command line debugger remotely.
I also asked on IRC:
<creikey> It should only work if the godot instance and the running game are on the same subnet
<creikey> there might be a way to manually configure from command line when running the game on the client the IP for remote debugging...
<creikey> yes in fact there is after looking at the output of --help
<creikey> you can run the godot game on the client with the argument --remote-debug [IP of computer][some open port I believe
<iFire> I made a patch for listening to remote machines but it's very janky
<iFire> https://github.com/fire/godot/tree/debug_listen feel free to make it great
<iFire> usecase is mobile debug
<iFire> .. over the network
<creikey> yeah, it seems like the command line flag for remote debugging is useless without that feature :\
<creikey> iFire: what port does it listen at?
<iFire> the on you tell it to
<iFire> in the editor settings
<iFire> the more problematic part is doing the same in the command line of the debugged application