Nelson Mandela

[www.discogs.com] https://www.discogs.com/Various-One-Year-On-46664/release/3974732 features a collaboration with Queen, but it looks like Mandela has prior releases.

His other releases and compilation appearances are all political speeches or use of his speech on tracks. But then so is that one:

[www.queenpedia.com] http://www.queenpedia.com/index.php?title=Invincible_Hope
"The song features extracts from Nelson Mandela's speeches."

Not sure it meets the "intentionally joined the collective whole of the band" rule. Sure, Mandela intentionally put on a benefit concert with Queen on the bill, but it's not clear if he made an effort to participate on the track or if producers just accessed a speech archive on their own initiative. In this live version where he's on stage and they bring a lectern for him, he doesn't use it and they just walk off while the recording of his speech plays:
[www.youtube.com] https://www.youtube.com/watch?v=g0rtq-8PQXw