Add an attribute to filter accounting data?

[Stefan Möding]

Hi!

We are using multiple Radius accounts to monitor the Freeradius server: is
it answering at all, avg. time to process an auth request, avg. time to
process an acct request, ...

These users would generate a great deal of data in the accounting logs (we
use the SQL driver to put it in a database).  Currently I have something
like this in the accounting configuration to filter for one user:

if (&User-Name != "radmonitoring") {
  sql_acct
}

I was wondering if it would be easier to add an additional attribute to
the user so I could use that attribute as the filter condition.
Advantage: it could work for multiple users without touching the config.

Has anybody done something like this?
What attribute would be a good pick?

Thanks!
-- 
Stefan