Hello, Kostas. I believe the best way to do that is to use stored procedures, if your DB server supports them. Then you can replace the accounting query strings in sql.conf to something like: "CALL accounting_start_procedure(attributes_you_want_to_pass)", and compose a stored procedure that will process the passed attributes and write to whatever tables you need.
I can give you a MySQL example, if you're interested. - List info/subscribe/unsubscribe? See http://www.freeradius.org/list/users.html
