SSL-ing mp3 files from a static non-ssl site?

Hi there; I’m trying to help a charity who are stuck with terrible, non-ssl hosting.
They have a few mp3s on a podcast, statically hosted. They are VERY untechnical and need to stick with what they’re doing. Can’t persuade them to move.

However, the mp3 files need to look like they come from a secure site for the Alexa/Echo Dot to play them (ridiculous, right?).

I’ve read all the FAQs and as far as I understand it, while Cloudflare won’t cache the mp3 files on the free plan, if I help them Cloudflare-ify their domain, if someone requests, it’ll grab it from the non-ssl site and serve it as a valid tls-certified file?

First post, please feel free to move to better category if needed.

Yes you are right. That SSL setting is called “Flexible” in the CF control panel.

If it’s a non-profit, you can probably get hosting for free - with ssl. Can you post the site for us to see?