For anyone interested, there's a Sailfish OS app to control the Gemini's phone-alert LEDs in the Jolla Shop. It's called "Funzel" and it defaults to the Knight Rider scheme. (What would be really cool would be if it also announced the name of the caller or the number calling in William Daniels's voice.)
Anyway it's there and it works at least to some extent. Well, the test with the lights doing the Knight Rider thing does -- I haven't seen it during an actual phone call yet.