I'd like to add that what was considered to be a "large" file six years ago when this suggestion was added is probably no longer considered a large file by 2022 standards. Internet speeds have increased dramatically since then. The remote connection is sluggish and slow even for small file transfers. 

I understand that having a secondary admin with their own Yubikey provides some redundancy, not only with regards to the hardware key but also in case someone gets hit by a bus.

But ALSO having a backup Yubikey in a locked, safe location somewhere brings extra convenience and does not compromise security.

Having a second admin account for the same user with a backup Yubikey is a hacky workaround. Many other services (Google, GoDaddy, Lastpass, AOL) have this capability. There is no reason why Connectwise can't do this.