That would let you quit rclone using the remote control...
So you'd run rclone as normal but with the --rc flag
rclone mount .... --rc
Then you could run
rclone rc core/quit
to quit rclone which should be enough to unmount the FS.
If you are running batch script simultaneiously then you would need to give each rc a different port with --rc-addr localhost:12345
SignalSend sounds like a reasonable solution if it works for you