Well, now I feel silly. I tried "vlc://quit" before without success. It must have been something in my syntax at the time because now it works flawlessly.
Thanks in advance. I've been Googling for a solution for the last couple of days without success. I have a batch file that ping scans the local network looking for cameras, and for every reply it starts an instance of VLC. My issue is that there are a couple of other devices, whose IP's can change, ...