OK, I now get the question clearly.
Here is a thought that is a bit converted but will probably work.
Create Sync table of your employee file in the same app and set the userid to be the Key field. The userid field will come across in the sync probably in the form of an email address in text format. Sync across the userid and the manager's userid.
Create a formula text field for the userid in text format on the employee file
ToText([Userid of Employee])
and then use that in a relationship to pull down the managers userid and call in [Current Users Manager userid in text format]. Once again, it will be in text format, so make a formula user field called
[Current Users Manager userid]
with a formula of
ToUser([Current Users Manager userid in text format])
Now you can filter your report with
[manager userid]
is equal to the value in the field [Current Users Manager userid]