I recently bought a second Yubikey and wanted to go through my accounts to add it as a backup; you know, have one locked up so that if I ever break my primary,

I recently bought a second Yubikey and wanted to go through my accounts to add it as a backup; you know, have one locked up so that if I ever break my primary, I'm not SOL. Not only do only about half a dozen services I use actively support hardware security keys, even fewer support enrolling more than one. Worse, many only support SMS 2FA as the backup option, which I just can't abide.