Form 2848 is a red herring.  Check the instructions to Form 4506-T.  I have helped a fiduciary do this and it worked, but I made sure the Form 56 had also been filed. 

Documentation. For entities other than individuals, you
must attach the authorization document. For example, this
could be the letter from the principal officer authorizing an
employee of the corporation or the letters testamentary
authorizing an individual to act for an estate.