custom passphrase to unlock

Hi, I was wondering if it would be possible to supply a flag that would prompt the user for a custom passphrase that would then be used to unlock the screen, instead of the user's actual password.

Why this might be useful:

 1 - You've locked your machine and left the building, but need to run a few user scripts. You could then message your colleague to unlock your machine and run said scripts using the custom passphrase, without compromising your actual password or giving them elevated priveleges (via sudo).

 2 - If you forget the passphrase you set, you can still unlock the machine by switching to a different tty and killing the process using regular elevated priveleges.

I understand that remote logins were invented for my first reason, but many workplaces are managed through subnets and makes access hard.

Why this might not be useful:
 - Security issues? I genuinely can't think of any except if the custome passphrase is weak.