my thought:
powershell feeds data into a webservice. Each computer has policy wit a script that queries the webservice everyday with its primary user and computername or other local values. (we use PHP for this kind of webservice at my company). in response it gets back a value for "manager name" which it writes into the registry.
like
DWORD Valuename: manager: Value: Jsmith
the second part of that policy is a custom inventory for that registry value that adds it to the custom inventory of that computer record. for the ssake of example lets call that custom inventory table "manager_name"
That way when you are making your filters all you would have to do it is set your SQL based filter to select all computers where manager name =jsmith as an example.
if the computer checks the webservice on a schedule, it will write the current managers name into the registry and report it), then it will dynamically become a member of the current users managers filter.
anyway that's how i would automate such a thing. It might seem commplicated to set up initially but has the advantage of being truly automated and hands off.
thanks