Colin,
Because you selected by-nc for your license, no one can use it commercially, so there’s no way they can use the share-a-like license.

If I can offer a solution, you could reupload this as a “sample” and select “cc-by” which accomplishes what the share-alike license does. Then a quick note to septahelix, and he could change the sample source to the new upload (with cc-by), making it a seamless change of licenses.

ps. The link you have for the info on the share-alike license has two extra characters at the end which sends it to an error screen.