Hi Mike,
i asked this questions a couple of weeks before.
Here the answer from CISCO.
Currently this feature is not there, you cannot use filters based on admin created attrbutes,
An enhancement is already open:
CSCui17182 <https://cdetsng.cisco.com/webui/#view=CSCui17182> <http://wwwin.cisco.com/ops/infra/pds/cbms/cdets/legend.shtml> ACS user filtering using custom attribute
Supposed to be included in 5.5, but it was not, so you can look forward to it on future ACS patch.
Save this ID on the bug search and you will get a notification.