Is this something you need to do on a regular basis, such as a backup person for a specific user?  There are workarounds to do most anything, but they can be unmanageable if you need to do it for dozens of users.  Describe your situation, there's probably a solution.  Maybe it's a special SYS FWD path when this user's in DND, maybe we need a phantom ext and CRA.
If you need to do it for a crowd of people you're best served by saying it can't be done, but for a few it's not bad.