Just like anything in Linux, you can do it at different levels. This is just one possibility. However, doing this isn't as simple as just running a command. You need to know what you're doing, so you can undo it if need be. For this reason, my answer will get you most of the way and provide links to get you the rest of the way.
REROUTING
First, you need to set up a stream to that output. To do this, you use pulseaudio. This is the program that supplies the audio stream to the applications. It works in terms of sources(inputs) and sinks (outputs).
streams are what connects them. You can think of it as a patch-cord. That is really all pulseaudio is. If youve ever seen a modular synthesizer, pulseaudio is the software version, except it doesn't change the audio. It just directs it.
You can learn more and get the commands you need here. Its alot, but that is a good thing. Look through the contents at the top and find the sections you need. I suggest you bookmark it. It will pay in diviends, I promise.
AUTOMATING
From there you can edit ~/.bash_aliases so that the command to open that app also switches streams (or moves the current stream). Look at the aliases set in ~/.bashrc lines 78-84 to see what I mean about the alias-to-add-functionality concept. If you don't want to mess with setting up a stream, you can just move the sink-input to a different sink.
NOTE:
Just in case you can't locate ~/.bashrc, it is because it is hidden. You need to run the ls command with an -a option to see files that start with a period.
