There really is nothing that complex going on in it. All you need is to make a mapped key that sends your corresponding ingame binds for Target Focus and Interact With Target. Both of those are found under "Targetting" in your WoW keybinds. Most likely you'll want to make ISBoxer send the commands to "all W/o current" so your lead toon doesn't also try to target and IWT it.

Then just make sure to set the brewpup as focus on all of your toons and it should function.