Recording post auth sql data

Hi, Hope this is a quick request for someone to answer, been googling and can't find the reply. I've altered the post-auth sql recording data a bit from the standard schema - I wanted to record some of the details of the request packet without relying on the NAS to do "proper" accounting, which I haven't got into yet. I'd quite like to record the attribute ClientShortname as referred to by the clients.conf file, but expansion of '%{request:Client-Short-Name}' didn't seem to work - blank string. Can I do this? Sometimes the "Nas-Identifier" attribute reported by the NAS isn't all that useful and the local definition in the clients file would be better. Thanks Andy