It's been done already, "Delegated Event Signing". It has poor support from relays and clients. Nostr Connect is a lot simpler.
nostr:npub108pv4cg5ag52nq082kd5leu9ffrn2gdg6g4xdwatn73y36uzplmq9uyev6
A better plan: allow limited grants of authority to be assigned to a server with a different key. It does not sign as you, but it is authorized to act on your behalf in a limited way.
Probably by your signing their key, like the PGP web of trust.
