Actually there is a method that you could use to lock UTXOs that is a kind of 2FA and that is by using a P2SH script that requires both a signed public key and a "revealed secret" (in much the same way as I've designed for doing Atomic Cross-Chain Transfers or ACCTs).

Of course you wouldn't want to trust some 3rd party for this but instead have some offline device providing the hashes and secrets for you (such as a mobile phone that has been placed in a Faraday cage).

Basically this would give you a way to have your keys on your online computer but still make things safe by having the secrets and hashes generated offline.