Setting recursive rights to folders as an Exchange admin

I have Users that have 100's of folders under one folder and I need to set rights to those folders to another user.  I know that I can use

 Get-MailboxFolder -Identity AttorneyA:\Cabinet -Recurse | add-MailboxFolderPermission -User SecretaryA -accessrights reviewer

but that only works for me if I am running this on my mailbox.  An admin can not run this for other mailboxes.  I don't understand how if I can make this work as an Exchange admin for another user.  I thought maybe login as the user and run it, but how do you run Exchange powershell as the user.  We currently go to each folder and set these rights manually and there must be a better way.