A PIN would do nothing to keep a user from being tricked into authorizing an attacker's login.
I think anyone who would blindly use your proprietary two factor solution that makes it easier for end users to authorize other people to log in would be silly.
'No 2FA' is the real silly one here. Any 2FA is so much better than no 2FA, and usability has been a big issue so far in 2FA adoption.