Thank you for the confirmation. Unfortunately, there is no possibility to create a business unit like you need only by means of membership rules. The thing is that value references resolve into the value of the currently logged on user. As such, the unit can only contain the accounts that their primary SMTP address set to the userPrincipalName of the logged on user.
To achieve the desired, you can use a scheduled task that will set a specific AD property to a certain value (e.g. set Description to mismatch) and then use the corresponding membership rule in your business unit. For example:
Business unit membership rule