Have NSSavePanel use ".jpg" instead of ".jpeg" for file extension?

How can I get NSSavePanel to use the extension ".jpg" instead of ".jpeg" in my app's save window?

My NSDocument subclass can export images and over the years I've gotten tons of requests for the extension for JPEG images to default to ".jpg" in the save window. I'm not sure how to make this happen though - I can't change the UTType at runtime, so the preferredFilenameExtension would return something other than ".jpeg", and NSSavePanel doesn't seem to send the right messages to my document for me to influence it. Yet, I know it can be done because Preview.app uses ".jpg" as its default extension when choosing the "JPEG" format.

What's the magic I'm missing?