Sorry for being late. Sadly it doesn't work for nostr keys.😔

I turned to holding the key as is in a password manager.

NoStranger

 as my client and it does not generate mnemonic phrases. Have you tried the solution with 

[1]:  https://github.com/mikedilger/gossip

nostr

Generating a NIP-06 Seed phrase from an existing private key

I have the same problem. I use [gossip][1] as my client and it does not generate mnemonic phrases. Have you tried the solution with `bx` from **bitcoin.stackexchange.com**? 

[1]:  https://github.com/mikedilger/gossip