Thanks, Joe, for asking!

I should give some added context (if anyone has suggestions):

* I run a small "filk" (science-fiction folk) publishing label in the states.
* There is a song we would like to release on a CD that's a derivative work of one of Cyril's songs (adapting his melody to new lyrics).
* In previous years, people in our community releasing this song have just asked Cyril directly for permission in-person — and verbally. He always enthusiastically gave that permission.
* Unfortunately, while we have witnesses to Cyril giving that verbal permission in the past — we don't have any written documentation that could be taken to a giant music corporation to grant permission.

If anyone has any suggestions or tips, I'm very appreciative. We may also splurge to talk to a music lawyer about whether a compulsory license may apply here.