How to prioritize 3.5mm if a device is plugged in, but otherwise fall back to a different device?

[SpencerDub]

Presently, I have my device set up to output to what I'm going to call the "built-in" speakers (the default ones that came with the WM8960, connected via a white plastic 4-pin connector). pactl list sinks currently says analog-output-speaker: Speakers, and Active Port: analog-output-speaker.

Right now, this works great! However, as I'm building this into a device, I'd like to tweak the settings so that when a device is connected via the 3.5mm jack, that device takes precedence, and the "built-in" speakers are muted. If there's no device plugged in to the 3.5mm, it falls back to the built-ins.

I believe the answer to this lies somewhere in the Pulse Audio configuration, but I have no idea where. Is this possible? If so, how can I do it?

Thanks!