> I was imagining the message encoded in clear text, not encrypted form, [...]

I was considering that, but I came to the conclusion that it would be an exceedingly poor choice.

Steganography is there to hide that a message has been sent at all. If you make it do double duty as a poor-man's encryption, you are going to have a bad time.

> As such, I approached it as a toy problem, and considered detection by savvy parties to be a feature, not a bug; I imagined something more like a pirate broadcast than a secure line, and intentionally ignored the presumption about the message being encrypted first.

That's an interesting toy problem. In that case, I would still suggest to compress the message, to reduce redundancy.