I'm not an expert in this area, but there is supposedly a definitive technical limitation with NFS limiting support of soft quotas. The architects of NFS did not implement a return call to indicate "I wrote your file, but..."
The only return codes from a NFS server indicate success or failure of the request. You would have to lobby with the architects of both NFS client and server software to ask them to add this for you - Netapp is only on one side of this coin.
The previously posted idea of periodic "quota reports" and sending email or other nastygrams to "soft limit" offenders is not a bad idea, although not as nice as what we all really want.
Realistically, messages at login are almost always ignored. Most of our users login once per month or so and just lock their screens nightly. You really need more frequent notification than once at login, and that is what soft quotas give you, so be carefull for what you ask...
We're playing in a standards-based arena, and are on the field with zillions of other teams. It's good to ask for improvements, but change is likely to be slow.